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Rookies

By Bill James

May 28, 2013

I recently had the following question in "Hey, Bill":

Bill --If you were to take the average player's rookie season (i.e., the season that the player last qualified for ROTY award), how much improvement will there be by that player's peak season? Is it anything like useful to make a remark like, "Player X has 15 WS in his rookie year--we can expect him, on average, to have a peak season at some point of 25 WS"? If one season isn't enough, at what point would we have enough seasons to make a useful general prediction as to eventual peak? After 1500 PA, say?

To which I replied, at the time:

Any answer you could give, I think you'd have to give with numerous qualifications, but let me see what I can do. First, let's exclude pitchers, since a very high percentage of rookie pitchers are unable to sustain the workload, and basically burn out after one season. Second, we'd have to exclude players who get a full shot as a rookie, but don't truly establish the level of ability necessary to keep a job.

From that point on, you'd get very different answers from a 21-year-old rookie than from a 25-year-old rookie. I'll try to do some relevant research and edit this answer later on.

Ok, I have done some research here, so let me report on that. . .I thought the question was worthy of a little work. I have a spreadsheet of career records. ..a kind of a "spreadsheet encyclopedia" that I use for projects like this. I took that file, and eliminated from it:

1) All players who played before 1950 (even one game before 1950), and

2) Players who have played since 2011 (2011, 2012 or 2013), since those player may not yet have complete careers.

3) All players who played less than 800 games in their careers.

This third elimination creates a major selection bias in the data, which makes these players who are studied here quite different from all rookies, and limits our ability to generalize what we learn from doing this. (On the other hand, not restricting the study group would cause other problems which, in my judgment, would be much worse, so. . ..six of one, half-dozen of the other. Doing the study this way, you learn quite a bit but you can’t generalize it reliably because of the selection bias. Doing the study the other way you wouldn’t learn anything to begin with.)

Anyway, I limited the data to players who played 800 games, so. . Al Weis is in, Rick Leach is out. You have to draw a line somewhere. To illustrate what I have done, let’s take all players who were rookies at the age of 18.

Since 1950 there have been three players who played 800 games and whose last rookie season was at age 18: Wayne Causey (1955), Ed Kranepool (1963) and Robin Yount (1974). This is what those three players did in their first seasons:

First	Last	YEAR	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
Wayne	Causey	1955	68	175	14	34	2	1	1	9	17	25	0	1	.194	.269	.234	.504
Ed	Kranepool	1963	86	273	22	57	12	2	2	14	18	50	4	2	.209	.256	.289	.545
Robin	Yount	1974	107	344	48	86	14	5	3	26	12	46	7	7	.250	.273	.346	.619

And here is that with the average performance of the three:

First	Last	YEAR	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
Wayne	Causey	1955	68	175	14	34	2	1	1	9	17	25	0	1	.194	.269	.234	.504
Ed	Kranepool	1963	86	273	22	57	12	2	2	14	18	50	4	2	.209	.256	.289	.545
Robin	Yount	1974	107	344	48	86	14	5	3	26	12	46	7	7	.250	.273	.346	.619

		1964	87	264	28	59	9	3	2	16	16	40	4	3	.223	.266	.302	.568

On average, the 18-year-olds hit .223 with a .568 OPS in their rookie season. In their second seasons, they improved to an average of .255 with a .667 OPS:

First	Last	YEAR	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
Wayne	Causey	1956	53	88	7	15	0	1	1	4	8	23	0	0	.170	.237	.227	.464
Ed	Kranepool	1964	119	420	47	108	19	4	10	45	32	50	0	1	.257	.310	.393	.703
Robin	Yount	1975	147	558	67	149	28	2	8	52	33	69	12	4	.267	.307	.367	.674

		1965	106	355	40	91	16	2	6	34	24	47	4	2	.255	.301	.366	.667

They relapsed a little in their third seasons:

First	Last	YEAR	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
Wayne	Causey	1957	14	10	2	2	0	0	0	1	5	2	0	0	.200	.471	.200	.671
Ed	Kranepool	1965	153	525	44	133	24	4	10	53	39	71	1	4	.253	.303	.371	.675
Robin	Yount	1976	161	638	59	161	19	3	2	54	38	69	16	11	.252	.292	.301	.593

		1966	109	391	35	99	14	2	4	36	27	47	6	5	.252	.301	.332	.632

Here we have a choice. .. here I had a choice, actually; you are pretty much stuck with the choices that I made. Wayne Causey was a Bonus Baby with the Baltimore Orioles in ’55 and ’56. The rules of the time required that a player getting a decent bonus had to spend two years on the major league roster (to discourage the signing of players to large bonuses), but after two years the player could go out to the minor leagues. Causey spent his two seasons with the Orioles, then went to do his minor league work, and did not play in the majors in 1958, 1959 or 1960, just becausey.

I could, then, have grouped Causey’s next major league season either as his fourth major league season, third season after the rookie season, or as his age-24 season, grouping him with Kranepool in 1969 and Yount in 1980. I decided to group him with other players playing their fourth season, third season after the rookie year. It doesn’t ordinarily matter much, because most players don’t have three-year gaps in their careers, and the results you would get from grouping them one way would be essentially the same as the results you would get from grouping them the other way, but. . .. this is the way I chose to do it.

So this is what these three players did in their fourth seasons, and in several seasons following that:

First	Last	YEAR	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
Wayne	Causey	1961	104	312	37	86	14	1	8	49	37	28	0	0	.276	.348	.404	.752
Ed	Kranepool	1966	146	464	51	118	15	2	16	57	41	66	1	1	.254	.316	.399	.715
Robin	Yount	1977	154	605	66	174	34	4	4	49	41	80	16	7	.288	.333	.377	.710

AVERAGE	Year 4	1968	135	460	51	126	21	2	9	52	40	58	6	3	.274	.329	.390	.720

Wayne	Causey	1962	117	305	40	77	14	1	4	38	41	30	2	0	.252	.340	.344	.684
Ed	Kranepool	1967	141	469	37	126	17	1	10	54	37	51	0	4	.269	.321	.373	.694
Robin	Yount	1978	127	502	66	147	23	9	9	71	24	43	16	5	.293	.323	.428	.752

AVERAGE	Year 5	1969	128	425	48	117	18	4	8	54	34	41	6	3	.274	.325	.388	.713

Wayne	Causey	1963	139	554	72	155	32	4	8	44	56	54	4	2	.280	.345	.395	.740
Ed	Kranepool	1968	127	373	29	86	13	1	3	20	19	39	0	3	.231	.271	.295	.566
Robin	Yount	1979	149	577	72	154	26	5	8	51	35	52	11	8	.267	.308	.371	.679

AVERAGE	Year 6	1970	138	501	58	132	24	3	6	38	37	48	5	4	.263	.309	.361	.670

Wayne	Causey	1964	157	604	82	170	31	4	8	49	88	65	0	1	.281	.377	.386	.763
Ed	Kranepool	1969	112	353	36	84	9	2	11	49	37	32	3	2	.238	.307	.368	.675
Robin	Yount	1980	143	611	121	179	49	10	23	87	26	67	20	5	.293	.321	.519	.840

AVERAGE	Year 7	1971	137	523	80	144	30	5	14	62	50	55	8	3	.276	.341	.434	.774

In Year 7 these three players averaged .276 with 14 homers, 62 RBI, 80 runs scored and a .774 OPS—a long step forward from what they had done at age 18:

First	Last	YEAR	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
AVERAGE	Year 1	1964	87	264	28	59	9	3	2	16	16	40	4	3	.223	.266	.302	.568
AVERAGE	Year 7	1971	137	523	80	144	30	5	14	62	50	55	8	3	.276	.341	.434	.774

Of course, a cadre of three players doesn’t really mean anything; I’m just using this small group to illustrate the process. These three, driven by Yount, actually continued to improve their OPS past the 7^th season, although their playing time began to decline:

First	Last	YEAR	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
Wayne	Causey	1965	144	513	48	134	17	8	3	34	61	48	1	3	.261	.341	.343	.684
Ed	Kranepool	1970	43	47	2	8	0	0	0	3	5	2	0	0	.170	.250	.170	.420
Robin	Yount	1981	96	377	50	103	15	5	10	49	22	37	4	1	.273	.312	.419	.731

AVERAGE	Year 8	1972	94	312	33	82	11	4	4	29	29	29	2	1	.261	.323	.365	.688

Wayne	Causey	1966	106	243	24	58	8	2	0	18	31	19	3	0	.239	.318	.288	.606
Ed	Kranepool	1971	122	421	61	118	20	4	14	58	38	33	0	4	.280	.340	.447	.786
Robin	Yount	1982	156	635	129	210	46	12	29	114	54	63	14	3	.331	.379	.578	.957

AVERAGE	Year 9	1973	128	433	71	129	25	6	14	63	41	38	6	2	.297	.356	.481	.837

Wayne	Causey	1967	124	292	21	66	10	3	1	28	32	35	2	5	.226	.302	.291	.593
Ed	Kranepool	1972	122	327	28	88	15	1	8	34	34	35	1	0	.269	.336	.394	.731
Robin	Yount	1983	149	578	102	178	42	10	17	80	72	58	12	5	.308	.383	.503	.886

AVERAGE	Year 10	1974	132	399	50	111	22	5	9	47	46	43	5	3	.277	.352	.422	.774

Wayne	Causey	1968	79	148	10	22	2	1	1	11	14	12	0	0	.149	.223	.196	.419
Ed	Kranepool	1973	100	284	28	68	12	2	1	35	30	28	1	0	.239	.310	.306	.616
Robin	Yount	1984	160	624	105	186	27	7	16	80	67	67	14	4	.298	.362	.441	.803

AVERAGE	Year 11	1975	113	352	48	92	14	3	6	42	37	36	5	1	.261	.331	.370	.701

After year 11 Wayne Causey dropped out of the majors. After this, then, we are comparing apples with fewer apples. After that it is no longer a comparison of a consistent group of players:

First	Last	YEAR	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
Ed	Kranepool	1974	94	217	20	65	11	1	4	24	18	14	1	0	.300	.350	.415	.765
Robin	Yount	1985	122	466	76	129	26	3	15	68	49	56	10	4	.277	.342	.442	.784

AVERAGE	Year 12	1980	108	342	48	97	19	2	10	46	34	35	6	2	.284	.349	.433	.783

Ed	Kranepool	1975	106	325	42	105	16	0	4	43	27	21	1	1	.323	.370	.409	.779
Robin	Yount	1986	140	522	82	163	31	7	9	46	62	73	14	5	.312	.388	.450	.838

AVERAGE	Year 13	1981	123	424	62	134	24	4	7	45	45	47	8	3	.316	.382	.434	.816

Ed	Kranepool	1976	123	415	47	121	17	1	10	49	35	38	1	0	.292	.344	.410	.754
Robin	Yount	1987	158	635	99	198	25	9	21	103	76	94	19	9	.312	.384	.479	.862

AVERAGE	Year 14	1982	141	525	73	160	21	5	16	76	56	66	10	5	.304	.368	.451	.820

Ed	Kranepool	1977	108	281	28	79	17	0	10	40	23	20	1	4	.281	.330	.448	.778
Robin	Yount	1988	162	621	92	190	38	11	13	91	63	63	22	4	.306	.369	.465	.834

AVERAGE	Year 15	1983	135	451	60	135	28	6	12	66	43	42	12	4	.298	.361	.460	.821

Ed	Kranepool	1978	66	81	7	17	2	0	3	19	8	12	0	0	.210	.280	.346	.625
Robin	Yount	1989	160	614	101	195	38	9	21	103	63	71	19	3	.318	.384	.511	.896

AVERAGE	Year 16	1984	113	348	54	106	20	5	12	61	36	42	10	2	.305	.374	.492	.866

Ed	Kranepool	1979	82	155	7	36	5	0	2	17	13	18	0	1	.232	.287	.303	.591
Robin	Yount	1990	158	587	98	145	17	5	17	77	78	89	15	8	.247	.337	.380	.717

AVERAGE	Year 17	1985	120	371	53	91	11	3	10	47	46	54	8	5	.244	.331	.364	.694

The Group Average OPS goes all the way up to .866 in the 16^th season, but of course there is no valid comparison to the earlier averages, because the "group" is not the same as it was, and 80% of the playing time in the Year-16 group is accounted for by Robin Yount. After Year 17 Yount is all that is left of this group of three players:

First	Last	YEAR	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
Robin	Yount	1991	130	503	66	131	20	4	10	77	54	79	6	4	.260	.332	.376	.707

AVERAGE	Year 18	1991	130	503	66	131	20	4	10	77	54	79	6	4	.260	.332	.376	.707


Robin	Yount	1992	150	557	71	147	40	3	8	77	53	81	15	6	.264	.325	.390	.714

AVERAGE	Year 19	1992	150	557	71	147	40	3	8	77	53	81	15	6	.264	.325	.390	.714


Robin	Yount	1993	127	454	62	117	25	3	8	51	44	93	9	2	.258	.326	.379	.705

AVERAGE	Year 20	1993	127	454	62	117	25	3	8	51	44	93	9	2	.258	.326	.379	.705

OK; that’s just to explain the process of the research, make sure you understand the flaws and limitations of the method. Now we can get to the real research.

First, let’s look at the number of players who are rookies at each age:

Number of Players	Rookie Age
3	18
11	19
48	20
111	21
172	22
202	23
212	24
135	25
67	26
26	27
12	28
5	29
2	30

The peak age for rookiedom, in this study, is age 24. This study would skew slightly younger than all rookies, because we are only studying players who had careers of 800 games or more. If we included players who had shorter careers, more of them would have had their rookie seasons at ages 25 and up. But among players who go on to good careers, the peak rookie ages are 23 and 24.

As to the quality of the rookies, the highest quality is for the youngest players. Among 19-year-old rookies, there are only 11 players in the group, but three of those are in the Hall of Fame (Mickey Mantle, Bill Mazeroski and Al Kaline), and a fourth will be (Ken Griffey, Jr.) A fifth, Tony Congiliaro, would be in the Hall of Fame if he hadn’t gotten hurt and/or sick, and two others, Rusty Staub and Cesar Cedeno, had careers of near-Hall of Fame stature. Alex Rodriguez was a rookie at age 19, but he’s not in this data because he is still active. Players who play regularly at a very early age are generally exceptional players. This chart counts the number of Hall of Famers, by their ages as rookies:

Number of Players	Rookie Age	Hall of Famers	Percentage
3	18	1	33%
11	19	3	27%
48	20	12	25%
111	21	10	9%
172	22	7	4%
202	23	8	4%
212	24	2	1%
135	25	0	0%
67	26	0	0%
26	27	0	0%
12	28	0	0%
5	29	0	0%
2	30	0	0%

One-third of players who are rookies at ages 18 through 20 either are in the Hall of Fame or will be one day. That percentage drops sharply after age 20.

Turning our attention now to the question posed by the reader, which is the rate of improvement which may be anticipated from a group of rookies. . . .this chart summarizes the material given earlier, for the 18-year-old rookies:

PLAYERS WHO ARE ROOKIES AT AGE 18
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
3	1	87	264	28	59	9	3	2	16	16	40	4	3	.223	.266	.302	.568
3	2	106	355	40	91	16	2	6	34	24	47	4	2	.255	.301	.366	.667
3	3	109	391	35	99	14	2	4	36	27	47	6	5	.252	.301	.332	.632
3	4	135	460	51	126	21	2	9	52	40	58	6	3	.274	.329	.390	.720
3	5	128	425	48	117	18	4	8	54	34	41	6	3	.274	.325	.388	.713
3	6	138	501	58	132	24	3	6	38	37	48	5	4	.263	.309	.361	.670
3	7	137	523	80	144	30	5	14	62	50	55	8	3	.276	.341	.434	.774
3	8	94	312	33	82	11	4	4	29	29	29	2	1	.261	.323	.365	.688
3	9	128	433	71	129	25	6	14	63	41	38	6	2	.297	.356	.481	.837
3	10	132	399	50	111	22	5	9	47	46	43	5	3	.277	.352	.422	.774
3	11	113	352	48	92	14	3	6	42	37	36	5	1	.261	.331	.370	.701
2	12	108	342	48	97	19	2	10	46	34	35	6	2	.284	.349	.433	.783
2	13	123	424	62	134	24	4	7	45	45	47	8	3	.316	.382	.434	.816
2	14	141	525	73	160	21	5	16	76	56	66	10	5	.304	.368	.451	.820
2	15	135	451	60	135	28	6	12	66	43	42	12	4	.298	.361	.460	.821
2	16	113	348	54	106	20	5	12	61	36	42	10	2	.305	.374	.492	.866
2	17	120	371	53	91	11	3	10	47	46	54	8	5	.244	.331	.364	.694
1	18	130	503	66	131	20	4	10	77	54	79	6	4	.260	.336	.376	.712
1	19	150	557	71	147	40	3	8	77	53	81	15	6	.264	.329	.390	.719
1	20	127	454	62	117	25	3	8	51	44	93	9	2	.258	.327	.379	.706

Here is the parallel data for the 19-year-old rookies—the group including Mantle, Kaline, Griffey, Cedeno, Staub, etc.:

PLAYERS WHO ARE ROOKIES AT AGE 19
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
11	1	103	339	39	88	14	3	7	35	27	52	6	4	.260	.317	.378	.694
11	2	113	412	61	119	20	4	13	56	36	60	10	5	.288	.346	.453	.799
11	3	125	434	63	122	22	4	15	67	46	66	13	6	.282	.351	.456	.808
11	4	121	434	65	124	21	4	15	65	41	63	11	5	.285	.347	.457	.804
11	5	139	483	68	136	24	4	17	69	57	70	10	5	.281	.358	.455	.813
11	6	142	509	80	149	25	3	21	78	59	70	11	5	.293	.368	.478	.847
11	7	132	461	65	128	21	4	16	61	61	61	12	4	.277	.363	.443	.805
11	8	126	446	70	121	20	4	17	64	58	65	13	4	.271	.356	.448	.804
10	9	120	442	71	125	20	4	20	68	48	64	11	3	.283	.356	.481	.836
10	10	124	441	67	121	20	3	17	64	49	60	11	4	.274	.348	.451	.800
10	11	136	474	71	133	21	4	21	77	63	66	12	4	.281	.367	.474	.841
10	12	116	384	56	102	16	2	15	56	53	51	5	2	.266	.356	.433	.789
9	13	119	389	52	106	20	1	13	55	46	52	5	4	.272	.352	.434	.787
9	14	108	356	48	97	17	1	13	55	49	51	5	3	.273	.363	.439	.802
8	15	102	347	46	94	17	1	12	49	37	48	6	2	.271	.343	.433	.776
7	16	111	377	49	103	16	1	16	59	42	53	5	2	.273	.348	.448	.796
7	17	89	284	38	74	13	1	12	41	43	47	1	1	.260	.358	.444	.802
4	18	124	402	58	108	19	1	17	59	67	63	3	2	.269	.376	.450	.826
3	19	107	322	44	95	15	1	15	49	45	48	3	0	.294	.382	.485	.867
3	20	115	340	39	85	17	0	10	48	44	42	1	1	.249	.338	.394	.731
3	21	123	353	40	88	18	1	12	50	47	55	1	1	.248	.338	.401	.739
2	22	56	85	4	19	3	0	1	13	7	13	0	0	.218	.273	.271	.544
1	23	54	45	2	12	3	0	1	8	10	4	0	0	.267	.400	.400	.800

Again, we can see that these players had a 150-point increase in OPS over their first six seasons, but we are still dealing with a very small group of players. As the groups get bigger, of course, the year-to-year data stabilizes.

In our data there are 48 players who were rookies at age 20. Twelve of those were Hall of Famers as well: Eddie Mathews, Roberto Clemente, Willie Mays, Ron Santo, Orlando Cepeda, Harmon Killebrew, Frank Robinson, Hank Aaron, Brooks Robinson, Johnny Bench, Rickey Henderson and Roberto Alomar. Several of the other 36 were near-Hall of Famers or will be Hall of Famers, like Joe Torre, Gary Sheffield and Ted Simmons. This chart summarizes the average performance by year of service of players who are rookies at the age of 20:

PLAYERS WHO ARE ROOKIES AT AGE 20
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
48	1	96	330	42	87	15	3	8	35	28	50	6	4	.262	.320	.396	.716
48	2	120	430	57	119	19	4	11	51	34	61	11	6	.276	.330	.415	.745
48	3	122	425	58	115	19	4	13	54	39	60	8	4	.271	.332	.429	.761
48	4	138	502	74	143	23	5	17	69	48	67	12	6	.286	.349	.453	.802
48	5	142	523	75	145	24	5	16	68	52	72	15	6	.277	.343	.433	.776
48	6	134	491	72	138	23	5	17	70	50	65	12	5	.282	.349	.450	.799
48	7	132	480	70	132	22	4	16	66	50	66	12	5	.276	.346	.441	.786
48	8	132	472	70	133	22	3	18	69	51	62	10	4	.281	.352	.455	.807
48	9	135	485	69	133	22	4	16	68	54	66	9	5	.274	.348	.431	.779
46	10	127	447	66	127	22	2	16	66	51	60	9	4	.285	.360	.450	.810
45	11	127	444	63	123	21	3	16	64	50	61	7	3	.277	.351	.443	.794
43	12	122	422	62	118	20	3	16	62	50	62	7	3	.279	.356	.454	.810
40	13	115	386	56	105	18	2	15	57	46	57	7	3	.274	.353	.448	.801
37	14	112	377	55	106	17	2	15	58	45	52	6	2	.282	.361	.461	.822
36	15	106	350	49	94	15	2	13	48	42	47	5	2	.269	.349	.432	.781
31	16	106	343	47	93	15	2	12	49	43	47	5	2	.271	.353	.429	.782
24	17	95	295	39	78	13	2	10	44	36	42	4	2	.265	.346	.423	.769
16	18	100	309	45	84	14	1	11	48	40	48	4	1	.272	.360	.435	.795
12	19	110	343	52	86	13	1	14	47	52	54	7	2	.250	.352	.411	.763
10	20	87	270	41	65	10	1	13	40	48	52	10	2	.240	.357	.426	.782
6	21	80	234	37	64	12	1	9	32	39	37	7	3	.275	.380	.446	.826
3	22	109	365	48	84	13	1	7	39	62	58	12	4	.229	.343	.334	.676
2	23	104	325	46	74	13	2	9	39	58	61	13	4	.228	.347	.358	.706
1	24	72	179	40	40	6	1	5	16	38	47	8	2	.223	.371	.352	.723
1	25	30	72	7	15	1	0	2	5	11	16	3	0	.208	.321	.306	.627

These players started with an OPS of .716, and improved that over the next three seasons to the range of .800. Let’s focus on the strikeout and walk data:

PLAYERS WHO ARE ROOKIES AT AGE 20
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	BB per 100 Ks
48	1		330							28	50				56
48	2		430							34	61				56
48	3		425							39	60				64
48	4		502							48	67				71
48	5		523							52	72				72
48	6		491							50	65				76
48	7		480							50	66				76
48	8		472							51	62				82
48	9		485							54	66				82
46	10		447							51	60				84
45	11		444							50	61				81
43	12		422							50	62				81
40	13		386							46	57				81
37	14		377							45	52				87
36	15		350							42	47				89
31	16		343							43	47				90
24	17		295							36	42				85
16	18		309							40	48				84
12	19		343							52	54				97
10	20		270							48	52				92
6	21		234							39	37				107
3	22		365							62	58				107
2	23		325							58	61				95
1	24		179							38	47				81
1	25		72							11	16				69

We can see that the strikeout to walk ratio of a group of players continues to improve as long as the entire group stays together. After 9 years the group is changing, as players drop out of the league, but even after that, in the data that we have, the strikeout/walk ratio of the group continues to improve, although that effect could be caused by the players who have poorer strikeout/walk ratios dropping out, while the players who have good strikeout/walk ratios may stay in the league. But we can see in this group—and you can see in the other groups—that the strikeout/walk ratio continues to improve as long as we are able to study it.

The players who were rookies at age 21 include ten Hall of Famers: Carl Yastrzemski, Paul Molitor, Dave Winfield, Joe Morgan, Cal Ripken, Eddie Murray, George Brett, Rod Carew, Willie McCovey and Gary Carter. There are 111 players in this group, however, so the Hall of Famers are "only" 9% of the group. Other outstanding players who had their rookie seasons at age 21 include Barry Bonds, Tim Raines, Lou Whitaker, Dwight Evans, Harold Baines, Willie Randolph, and Keith Hernandez. The group also includes, however, Jamie Quirk, Jerry Hairston, Dale Berra, Darrel Chaney, Alex Trevino, Rowland Office and John Ellis. Whereas the group of players who were rookies at age 20 averaged 1900 hits in the majors (1914, actually), 235 homers and an .827 OPS, those who were rookies at age 21 averaged 1500 hits (1518, actually), 163 homers and a .779 OPS. I’ll chart those averages at the end of the article. This is the average performance, by year of career, of the players who were rookies at age 21:

PLAYERS WHO ARE ROOKIES AT AGE 21
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
111	1	104	341	43	89	14	3	7	36	31	55	7	4	.260	.322	.381	.703
111	2	115	395	51	105	18	4	10	46	37	61	8	4	.265	.328	.402	.731
111	3	122	424	58	115	20	4	12	52	44	64	9	4	.272	.341	.417	.758
111	4	126	440	60	119	21	4	12	55	46	64	10	5	.270	.339	.413	.752
111	5	130	460	66	126	22	4	14	61	48	66	11	5	.274	.343	.430	.774
111	6	130	454	63	124	21	4	13	59	49	64	10	5	.273	.344	.424	.769
111	7	124	429	60	116	20	3	13	56	48	61	8	4	.269	.345	.421	.766
111	8	120	412	57	112	20	3	12	53	47	59	8	4	.272	.347	.420	.767
109	9	115	391	53	105	19	2	12	51	44	55	7	3	.269	.344	.419	.763
101	10	115	388	54	107	19	2	12	53	46	53	7	4	.274	.353	.428	.780
89	11	120	403	55	109	20	2	12	56	49	58	7	3	.271	.352	.420	.772
83	12	112	366	51	99	17	2	12	52	47	52	6	3	.270	.355	.424	.778
75	13	104	337	45	87	15	2	11	46	41	51	5	3	.259	.342	.410	.752
62	14	96	300	42	79	14	2	9	42	38	44	4	2	.264	.350	.414	.764
50	15	99	318	44	86	16	1	10	44	40	45	5	2	.269	.353	.422	.775
39	16	97	301	44	84	14	2	11	46	42	42	4	2	.278	.368	.443	.811
27	17	105	332	48	95	17	1	11	48	46	42	4	2	.287	.375	.447	.822
19	18	103	345	48	94	18	1	12	50	46	48	5	2	.273	.361	.439	.800
15	19	115	380	57	110	20	2	14	61	58	50	5	2	.288	.385	.460	.845
12	20	105	364	45	98	18	1	13	56	37	50	3	2	.268	.336	.428	.764
8	21	99	299	38	76	14	1	10	45	44	42	2	1	.255	.353	.407	.760
5	22	77	222	30	55	10	0	9	33	45	34	1	0	.248	.379	.422	.801
1	23	119	380	38	101	24	0	10	56	54	29	0	0	.266	.360	.408	.768

The one player in that group who played into his 23^rd season was Yastrzemski, while McCovey, Winfield, Baines and Bonds all made it to 22 seasons. Players who are rookies at age 21 have an average increase in OPS, over the following four seasons, of about 70 points. Here again, we see the consistent improvements in control of the strike zone as long as we are able to track that.

Among the 172 players in our group who were rookies at the age of 22, the seven Hall of Famers are Tony Gwynn, Luis Aparicio, Andre Dawson, Jim Rice, Barry Larkin, Reggie Jackson and Ryne Sandberg. Other players of note who had their rookie seasons at 22 include Pete Rose, Al Oliver, Rafael Palmeiro, Steve Garvey, Frank Thomas (Big Hurt), Dave Concepcion, Chili Davis, Bernie Williams, Bert Campaneris, Don Mattingly, Dale Murphy, Will Clark, Harvey Kuenn, Reggie Smith, Amos Otis, Frank White, Willie Horton, George Scott, George Hendrick, George Foster, George Bush, George Orwell, George Patton, George Washington, George Washington Carver, George Clooney, George Custer, George McGovern, George Stephanopoulos, Bobby Bonds, Dick Allen, Robin Ventura, Rocky Colavito, Bill White, Albert Belle, and Jermaine Dye. On the other hand, the group also included Woody Woodward, Jack Brohamer, Ken Boswell, Tim Flannery, Ed Herrmann, Daryl Boston, Russ Nixon, Tom Veryzer and Manny Lee. This is the average performance of this group, by year:

PLAYERS WHO ARE ROOKIES AT AGE 22
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
172	1	102	337	44	88	14	3	8	38	29	56	7	4	.260	.320	.389	.709
172	2	114	390	52	104	17	3	9	44	35	60	10	5	.266	.328	.396	.724
172	3	122	422	58	114	20	4	11	52	39	63	12	5	.271	.334	.413	.747
172	4	129	454	63	125	21	4	13	59	42	65	11	5	.275	.338	.423	.761
172	5	131	470	66	131	23	4	14	62	46	67	11	6	.279	.346	.433	.778
172	6	131	473	68	131	23	4	14	61	47	67	12	5	.277	.344	.426	.771
172	7	126	444	62	121	21	3	13	58	45	64	11	5	.273	.341	.423	.765
169	8	118	411	57	112	19	3	12	53	43	61	8	4	.273	.345	.423	.768
165	9	116	401	55	109	19	2	12	52	41	58	8	4	.271	.342	.420	.763
161	10	113	384	53	105	19	3	12	51	39	57	7	3	.273	.343	.425	.768
142	11	108	368	50	100	17	2	10	47	37	53	7	3	.273	.342	.415	.758
121	12	104	352	46	94	17	2	10	45	36	53	6	3	.268	.339	.410	.749
95	13	102	335	46	91	16	2	10	45	36	53	6	2	.272	.344	.419	.763
74	14	111	355	47	96	18	2	10	49	37	54	5	3	.271	.342	.417	.759
58	15	105	328	43	89	16	2	10	45	35	51	5	2	.271	.344	.419	.764
43	16	92	290	37	77	14	1	9	39	28	44	4	3	.266	.333	.411	.744
28	17	90	285	35	76	14	1	8	39	27	40	3	2	.268	.335	.414	.749
19	18	97	313	39	85	17	0	8	42	34	45	3	2	.271	.344	.403	.747
12	19	76	238	31	64	10	1	6	28	26	34	2	1	.271	.346	.392	.738
4	20	98	283	33	74	13	2	5	32	28	38	3	2	.261	.331	.372	.703
1	21	151	493	52	121	14	3	0	45	52	28	7	7	.245	.319	.286	.605
1	22	121	374	43	107	15	2	0	34	40	27	1	1	.286	.357	.337	.694
1	23	119	405	60	107	12	2	2	46	86	35	8	1	.264	.397	.319	.716
1	24	72	237	15	52	8	2	0	25	30	31	3	0	.219	.317	.270	.587

Here, of course, the player who lasts for 24 years is Pete Rose, and the overall improvement of the group after their rookie season is not discernibly different from that of the 21-year-olds.

Dealing now with the 23-year-old rookies. . .there were 202 of these, not a single one of whom was named "George". A lot of "Daves". . .Dave Rader, Dave Chalk, Dave Kingman, Dave Parker, Dave Anderson, Dave Henderson, Dave Hanson, Davey Johnson. The eight Hall of Famers in the group, alphabetically, are Ernie Banks, Lou Brock, Tony Perez, Kirby Puckett, Mike Schmidt, Ozzie Smith, Willie Stargell and Billy Williams, and the group also includes the two Houston superstars who might go into the Hall of Fame, Bagwell and Biggio. Other outstanding players are Parker, Fred McGriff, Murcer, Lynn, Oliva, Grich, Frank Howard, Nomah, Mark McGwire and Mo Vaughn, as well as Chicken Stanley, Terry Crowley, Ty Cline and Herm Winningham. Tony Oliva’s listed age may not be correct. This is the chart for the 23-year-old rookies:

PLAYERS WHO ARE ROOKIES AT AGE 23
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
202	1	105	341	44	89	15	3	9	40	32	59	8	4	.260	.325	.399	.724
202	2	119	391	51	103	17	3	10	47	37	63	9	4	.263	.328	.400	.728
202	3	124	419	56	113	20	3	12	52	40	66	10	5	.270	.336	.416	.752
202	4	126	430	59	116	21	3	13	55	44	69	10	5	.271	.340	.423	.764
202	5	127	431	58	116	21	3	13	56	43	69	9	4	.269	.338	.419	.757
202	6	121	404	54	109	20	3	12	54	43	63	8	4	.269	.342	.423	.764
202	7	116	387	52	103	19	3	12	52	40	61	7	4	.267	.338	.418	.757
200	8	111	363	50	97	17	2	12	50	38	59	6	3	.267	.339	.425	.764
183	9	106	348	47	94	17	2	11	47	37	56	6	3	.269	.342	.421	.763
157	10	102	331	45	89	16	2	11	45	35	53	5	3	.269	.342	.423	.765
133	11	103	332	44	89	15	2	11	46	36	54	5	2	.269	.343	.421	.764
108	12	104	327	44	88	16	2	11	46	39	53	4	3	.270	.351	.426	.777
81	13	99	315	42	84	15	2	11	45	34	52	4	2	.267	.342	.426	.769
62	14	104	333	46	89	16	2	11	48	39	55	5	2	.266	.347	.430	.777
47	15	100	324	43	85	15	1	12	46	34	56	4	2	.261	.336	.423	.759
27	16	116	372	47	97	18	2	12	52	35	60	4	2	.261	.331	.412	.743
16	17	101	338	44	88	16	1	12	46	32	54	4	2	.261	.330	.423	.754
13	18	91	273	32	68	13	1	7	32	24	46	3	2	.250	.316	.385	.701
6	19	77	231	30	60	12	1	5	27	24	41	2	1	.260	.332	.384	.717
2	20	73	105	7.5	25	5	1	3	16	11	23	0	0	.238	.307	.367	.674
1	21	72	183	25	60	8	0	6	33	22	22	0	2	.328	.400	.470	.870
1	22	77	200	14	51	12	1	2	29	25	25	0	0	.255	.338	.355	.693

We can see, then, that as the rookies get older, they are better prepared to compete in the major leagues as rookies. The OPS of the rookie class is .694 at age 19, .703 at age 21, .709 at age 22, .724 at age 23. But the potential of the class is going down, with their peak OPS (for the complete group) being .847 at age 19, .807 at age 20, .778 at age 22, and .764 at age 23. So the short answer to the reader’s query is, it depends on the rookie’s age. If he’s 19, you can guess that he’ll have something like a 100-point growth in OPS. If he’s an older rookie, then one’s expectations for improvement should be modest.

At age 24 we have our largest group of rookies, 212 of them. The Hall of Famers in the group are Wade Boggs and Carlton Fisk, and the group OPS never reaches .750 as long as the whole gang is together. Mike Piazza was a rookie at 24. Trying to find anyone else in the group who ever won an MVP Award. . ..Ken Boyer, Ken Caminiti, Kevin Mitchell, Jackie Jensen. I believe that is it.

PLAYERS WHO ARE ROOKIES AT AGE 24
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
212	1	100	312	40	82	13	3	7	35	27	50	6	4	.262	.322	.390	.711
212	2	116	385	51	102	18	3	9	45	36	59	8	4	.266	.329	.396	.725
212	3	120	409	55	110	18	3	10	49	38	62	9	5	.268	.332	.402	.734
212	4	127	436	59	118	20	3	12	54	41	65	9	5	.269	.334	.411	.744
212	5	123	421	56	112	20	3	11	52	41	65	9	5	.267	.333	.410	.743
212	6	124	421	57	113	20	3	11	53	41	64	8	4	.268	.335	.410	.745
211	7	118	397	53	105	19	3	10	51	40	61	6	4	.265	.335	.405	.740
208	8	114	372	49	99	18	2	11	48	38	58	6	3	.267	.337	.414	.751
198	9	104	331	45	89	17	2	10	43	34	53	5	3	.269	.339	.416	.756
170	10	105	333	44	89	16	2	10	44	36	53	4	3	.267	.341	.413	.754
145	11	98	304	40	80	15	1	9	40	32	48	4	2	.264	.337	.411	.748
117	12	94	287	38	75	14	1	9	39	32	49	4	2	.263	.340	.410	.750
86	13	96	284	36	74	14	1	9	39	32	47	3	2	.261	.338	.411	.749
58	14	94	283	38	75	13	1	9	39	33	46	3	2	.264	.343	.410	.753
44	15	80	235	30	60	12	1	7	29	26	40	3	2	.257	.334	.398	.733
24	16	84	245	33	63	12	1	8	33	30	38	1	1	.257	.339	.415	.754
16	17	90	262	34	68	12	1	9	37	32	42	2	1	.260	.343	.412	.755
11	18	77	221	27	56	10	2	6	30	29	35	1	1	.253	.341	.398	.739
6	19	89	221	27	57	9	1	7	33	28	36	2	1	.256	.344	.398	.742
3	20	107	262	26	64	14	0	9	43	23	54	2	1	.243	.309	.405	.714
2	21	79	177	13	44	7	1	3	24	18	44	5	1	.249	.322	.337	.659
2	22	40	72	5	15	2	0	1	10	8	17	1	1	.210	.292	.273	.565

The two players who started at age 24 and lasted 22 years were Carlton Fisk and Julio Franco. For purposes of this study I ignored any "pre-rookie" performance.

At age 25 the number of rookies who last as long as 800 games in the majors drops sharply, to 135. No one in this group is in the Hall of Fame, and also, no one in this group ever won an MVP Award. The best players in this group are Kenny Lofton, Brett Butler, Andres Galarraga, Moises Alou, Ron Cey, Bob Boone, Norm Cash and Lou Piniella. One notable thing is that, in this group, I think we have almost all of the greatest fluke seasons of the last 60 years. . .Norm Cash in 1961, Jim Hickman in 1970, Cito Gaston in 1970, Bill Mueller in 2003, Floyd Robinson in 1962, maybe Kevin Seitzer in 1987. There are a few Rookies of the Year in here—Piniella, Jimmie Hall, Tommy Helms, Bake McBride, Gary Mathews, Ron Kittle—but the Rookie of the Year Award often tends to be the career highlight for this group.

PLAYERS WHO ARE ROOKIES AT AGE 25
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
135	1	105	328	43	88	14	3	7	37	30	51	7	3	.267	.330	.394	.724
135	2	120	394	52	107	19	4	9	48	37	58	8	4	.272	.336	.409	.745
135	3	120	408	54	111	20	3	10	49	38	60	9	4	.271	.336	.408	.745
135	4	124	422	57	116	21	3	11	52	39	61	9	5	.275	.338	.414	.752
135	5	125	423	57	116	20	3	11	53	40	61	8	4	.273	.340	.415	.754
135	6	116	375	49	100	18	2	9	46	35	54	6	3	.268	.333	.403	.735
134	7	111	355	46	96	17	2	9	43	33	51	6	3	.270	.335	.404	.739
129	8	105	325	42	86	16	2	8	40	30	48	4	3	.265	.330	.394	.725
112	9	98	305	39	83	15	2	7	38	29	43	4	2	.273	.338	.403	.741
93	10	96	290	36	78	14	2	7	36	28	42	3	2	.270	.336	.401	.736
71	11	88	254	32	68	13	1	7	33	25	38	3	2	.266	.334	.403	.737
45	12	90	271	36	73	13	1	8	35	27	41	3	2	.268	.338	.411	.748
29	13	94	280	36	76	14	2	7	35	30	41	3	2	.272	.347	.410	.758
19	14	91	280	36	77	14	1	7	34	27	40	4	1	.274	.341	.408	.749
16	15	63	182	23	49	8	1	4	19	17	25	4	1	.270	.334	.384	.718
8	16	73	218	29	62	9	1	3	21	21	29	6	3	.286	.349	.380	.729
4	17	82	209	21	58	8	1	4	24	19	31	1	1	.276	.335	.371	.706
3	18	18	45	4	11	1	0	0	4	6	5	0	0	.254	.338	.299	.636
1	19	1	1	0	0	0	0	0	0	0	0	0	0	.000	.000	.000	.000

There are only 67 rookies in our study who were 26 years old, but two of those had near-Hall of Fame careers, Edgar Martinez and Maury Wills, and two did win MVP Awards, Maury Wills in 1962 and Elston Howard in 1963. A lot of guys who were pretty good. . .Jim Gentile, Jim Lemon, Vic Power, Phil Garner, Don Hoak, Donn Clendenon, Vic Davalillo, George Altman.

PLAYERS WHO ARE ROOKIES AT AGE 26
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
67	1	100	300	40	80	12	3	6	32	27	45	10	4	.265	.327	.386	.713
67	2	121	386	54	104	17	3	9	45	37	60	12	6	.270	.336	.400	.735
67	3	123	417	58	112	19	4	10	47	40	65	13	5	.269	.336	.404	.740
67	4	127	428	59	116	19	3	10	50	41	65	13	6	.272	.338	.406	.744
67	5	121	395	53	105	18	3	9	47	38	60	11	5	.265	.332	.395	.727
67	6	109	354	46	92	15	3	8	41	32	55	11	4	.259	.324	.386	.710
66	7	106	325	44	86	15	2	7	37	34	51	10	4	.265	.336	.387	.723
62	8	105	306	41	80	15	2	7	37	32	49	8	3	.263	.334	.396	.730
52	9	87	260	36	70	12	2	6	32	26	39	6	3	.269	.337	.394	.732
41	10	94	280	35	75	13	1	6	31	27	42	6	2	.268	.335	.389	.724
29	11	87	257	34	69	11	2	5	27	25	38	6	3	.268	.335	.386	.720
19	12	95	282	38	76	13	1	6	31	31	42	7	3	.269	.342	.385	.728
15	13	88	249	31	63	11	1	5	28	27	40	7	2	.253	.328	.356	.683
9	14	71	187	25	48	6	1	3	18	20	32	6	2	.258	.333	.358	.691
4	15	71	184	28	50	8	0	7	30	30	32	7	2	.273	.379	.429	.807
2	16	74	246	23	65	12	0	6	32	29	54	1	0	.262	.342	.382	.725

Here the selection bias—not including players who played less than 800 games in the majors in our study—here that issue is critical. Based on this, we would conclude that even players who come to the majors at age 26 show some improvement, over the next several years, as they adjust to the major leagues. But this may not be an accurate conclusion, as it may be that the 26-year-olds who wash out of the majors short of 800 games are going down by as much as these players are going up. We do know that some players who don’t get established in the majors until they are 26 still show some improvement over the following years.

Just finishing out the data now:

PLAYERS WHO ARE ROOKIES AT AGE 27 (26 of them)
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
26	1	109	344	49	94	15	3	6	37	29	53	11	4	.274	.330	.386	.716
26	2	117	382	49	104	17	3	9	40	31	54	13	4	.271	.328	.402	.730
26	3	125	430	59	120	21	4	9	48	38	59	14	6	.278	.336	.412	.749
26	4	135	473	61	127	23	5	10	53	41	63	13	6	.269	.328	.400	.728
26	5	117	381	49	98	17	3	9	43	34	54	9	4	.258	.321	.388	.709
26	6	111	364	51	98	16	3	9	46	34	52	8	4	.270	.336	.401	.737
26	7	119	406	51	107	19	3	9	45	33	57	7	4	.263	.321	.389	.709
25	8	98	310	42	82	14	2	6	32	27	44	8	3	.266	.327	.384	.710
21	9	94	280	35	70	10	2	5	30	28	41	6	2	.249	.319	.354	.673
16	10	77	218	27	58	10	1	6	27	24	31	2	1	.265	.337	.408	.745
10	11	71	217	29	56	12	1	6	26	23	32	2	1	.260	.331	.405	.736
5	12	73	196	23	53	11	1	4	28	18	32	4	2	.270	.331	.404	.735
1	13	131	335	42	102	20	2	3	33	38	58	2	0	.304	.378	.403	.781
1	14	142	489	54	131	26	4	10	66	40	65	3	2	.268	.328	.399	.726
1	15	101	256	25	65	13	1	6	37	27	36	4	0	.254	.323	.383	.706

PLAYERS WHO ARE ROOKIES AT AGE 28 (there are 12 of those)
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
12	1	76	194	24	49	8	2	3	17	20	26	5	3	.251	.320	.350	.669
12	2	93	269	38	74	14	1	7	35	29	37	8	4	.276	.347	.419	.766
12	3	106	338	45	91	18	3	7	40	34	42	8	3	.269	.337	.398	.735
12	4	114	344	43	91	18	2	8	38	36	47	6	3	.264	.336	.399	.735
12	5	117	351	46	93	17	2	10	45	39	53	7	4	.264	.339	.409	.748
12	6	121	384	49	105	18	2	11	50	39	58	7	2	.274	.341	.422	.763
12	7	111	342	46	92	17	2	9	41	36	50	4	1	.268	.339	.411	.750
12	8	105	302	37	77	14	1	7	36	31	45	3	1	.253	.325	.377	.702
11	9	82	215	25	53	10	0	5	24	22	35	3	1	.245	.322	.361	.683
8	10	75	201	24	49	11	1	4	23	21	32	4	3	.245	.321	.372	.692
5	11	83	200	21	49	7	1	5	21	21	28	4	1	.247	.319	.360	.679
4	12	61	158	21	37	6	1	3	17	18	28	4	0	.233	.315	.342	.657
2	13	54	147	27	41	6	0	6	23	24	22	24	2	.279	.379	.442	.821
1	14	96	255	49	70	10	3	7	35	43	25	25	8	.275	.381	.420	.800
1	15	47	43	4	10	2	0	1	6	13	8	2	1	.233	.411	.349	.760

PLAYERS WHO ARE ROOKIES AT AGE 29
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
5	1	124	389	53	105	16	6	10	50	36	56	9	3	.270	.330	.422	.752
5	2	133	465	59	125	21	5	13	68	38	70	9	6	.268	.324	.423	.747
5	3	136	481	56	131	21	3	13	59	46	72	8	5	.273	.337	.413	.751
5	4	137	463	58	119	21	3	11	57	50	71	9	5	.257	.330	.389	.719
5	5	129	434	52	111	19	3	11	52	39	59	7	3	.255	.317	.389	.706
5	6	109	324	30	80	13	3	6	38	30	56	5	1	.247	.314	.363	.678
5	7	108	318	35	78	11	2	9	40	25	44	5	2	.246	.300	.384	.684
5	8	80	187	20	45	8	1	4	21	18	25	3	1	.240	.309	.357	.666
3	9	39	59	11	13	1	0	1	5	4	11	1	0	.220	.264	.299	.564
1	10	65	141	20	34	8	0	2	10	24	14	6	3	.241	.352	.340	.692

PLAYERS WHO ARE ROOKIES AT AGE 30
#	Yr	G	AB	R	H	2B	3B	HR	RBI	BB	SO	SB	CS	Avg	OBA	SPct	OPS
2	1	71	167	24	52	12	2	3	20	8	14	5	1	.311	.347	.452	.799
2	2	122	336	37	85	19	2	4	39	19	27	7	5	.251	.293	.347	.640
2	3	113	302	32	78	9	4	4	31	21	20	4	2	.257	.303	.343	.645
2	4	128	418	41	94	17	1	5	28	22	36	3	3	.224	.264	.303	.567
2	5	109	247	26	66	7	2	1	19	15	16	4	5	.266	.305	.312	.617
2	6	119	342	33	82	12	2	1	26	25	21	3	2	.239	.292	.294	.586
2	7	86	171	16	39	6	0	2	12	12	13	1	2	.225	.273	.287	.559
2	8	83	189	19	42	7	2	3	19	14	29	0	1	.222	.271	.315	.586
1	9	62	95	18	23	5	1	3	8	13	19	0	1	.242	.333	.411	.744

The two players who were rookies at age 30 were Keith Lockhart and Bob Lillis, and the five who were rookies at age 29 were Jungle Jim Rivera, Dale Long, Gene Michael, Ron Coomer, and the little kid from the movie "42", Ed Charles. Our final chart summarizes the average career totals of the players, by the age at which they were rookies:

	Rookie Age
#	Rookie Age	G	AB	H	2B	3B	HR	RBI	BB	SO	SB	Avg	OBA	SPct	OPS
3	18	1938	6563	1793	313	59	135	768	603	757	99	.273	.362	.400	.762
11	19	2004	6842	1891	320	47	253	990	802	978	140	.276	.396	.448	.843
48	20	1988	6944	1914	316	52	235	958	744	969	144	.276	.390	.437	.827
111	21	1665	5628	1518	265	40	163	735	628	819	107	.270	.371	.418	.789
172	22	1560	5352	1453	250	38	150	682	527	793	116	.272	.374	.417	.791
202	23	1393	4577	1222	216	30	137	599	468	741	87	.267	.373	.417	.790
212	24	1367	4443	1181	210	29	119	557	441	693	78	.266	.365	.406	.771
135	25	1212	3878	1047	185	27	94	472	366	569	68	.270	.364	.404	.768
67	26	1155	3602	957	161	26	82	414	352	558	103	.266	.353	.393	.746
26	27	1145	3665	977	166	30	79	410	324	523	91	.267	.356	.393	.749
12	28	1074	3104	814	150	16	76	367	328	450	64	.262	.351	.394	.746
5	29	1015	3176	820	135	28	82	397	292	472	58	.258	.358	.395	.753
2	30	898	2298	570	93	13	24	203	147	192	27	.248	.306	.330	.636

COMMENTS (5 Comments, most recent shown first)

shthar
This pretty much confirms what I've figured out, the younger a player is when he makes the bigs the better.

And don't draft 27 year old rookies with the expectation of them being around more than a couple of years.
8:35 PM May 30th

bjames
I used this data because this was the data that I had organized in a fashion that could apply to the question. Win Shares would be good, but I don't have the right data organized in the right way. . . .and I don't have any fielding stuff I could use, at all. I think I probably could do the "age of rookies" study. Don't know if I should worry about "baseball ages" for that or whether the amateur researchers have corrected the record enough that older dates of birth can now be thought of as accurate.
12:09 PM May 29th

KaiserD2
This is a very thorough study which immediately reminded me of the big rookie study in one of the last annual Abstracts--maybe the last annual Abstract (I remember it's the one with a yellow cover)--whose conclusions were similar. (It also had a fascinating discussion about race which would be very interesting to update now.) I am left once again with a big chicken and egg question.

One can interpret the data to mean that a) the sooner you get a promising hitter into the majors, the better he will turn out to be. Or, one can interpret the data to mean that b) the greatest hitters are easily identified at an early age and thus rushed to the majors. I think either one of those things could be true, but I'm more inclined to believe a). The younger you are when big-league pitching becomes your norm, the better you are likely to get at hitting it. But I certainly can't prove that.

But if a) is true, then the structure of contemporary baseball has a big problem, because it's become significantly harder, it seems to me, to reach the majors at 19, 20 or 21, especially if you're a US citizen who has been to college. I think Kevin Youkilis might have been a hall of famer if he had gotten into the majors a few years earlier, but you never know. Indeed, it's frequently written that teams want to delay players' major league debuts so as to delay the day when they will become free agents.

I hope perhaps some day Bill can use his data base to track the average age at which players enter the majors and how that has changed.

DK
7:21 AM May 29th

Steven Goldleaf

Fascinating stuff—it’s merely logical that a player’s peak would flatten as his rookie year gets pushed later and later, but it’s fun seeing how much. What I’ve learned—or had reinforced—here is that an elderly rookie who has a good rookie season may be playing at or close to his peak, while a younger rookie almost certainly is going to improve. A side-question is: why have you expressed this in terms of OPS rather than WS? I used WS in my initial question because I thought that was the Gold Standard in summarizing stats, but it seems not. Was that too fond a goal, that you would develop a 2-digit summary, or are you hopeful that you can tweak WS such that an answer like this can be expressed in terms of WS? Should we give up on a 2-digit summary for the time being?

6:49 AM May 29th

Robinsong
Excellent study!
I thought the ratio of age 27 OPS to rookie OPS was interesting.
19 - 1.205; 20 - 1.127; 21 - 1.090; 22 - 1.087; 23 - 1.046; 24 -1.046;
25 - 1.029; 26- 1.031. A very consistent pattern, but the relatively small upside for all groups was also striking. Even the 19-year olds captured most of their upside by 20. Since the older rookies also start at a higher level, the gap in age 27 performance (.836 OPS for those who were 19 year old rookies vs .735 for those who were rookies at 26) is 13.7%. This difference is about twenty runs, which means about 2 wins or 6 Win Shares.

Another factor for projecting maximum Win Shares is playing time; rookies play less than 27 year olds.

Finally, a question: Could you do a similar analysis for fielding? My guess is that defensive skill peaks very quickly after the rookie year so that defensive Win Shares per game played would be very similar at 27 as when a rookie and that there is not a marked difference between though who came up early and those who arrived in the big leagues at 25 in defensive performance at age 27, but it would be interesting to study.
3:14 PM May 28th

Rookies

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