Can the National League Reverse a 10-Year Trend?

May 10, 2014

A look at the World Series winners over the last decade would suggest the National League has been the better of the two leagues. Since 2003, the NL holds a 6-5 edge over the American League in those critical matchups. However, even seven game series provide too small of a sample to declare which league has been best in those seasons, especially when you consider depth in addition to simply the best team.

Interleague play in the regular season has been around for 17 years, and the volume of games teams from each league play against each other provides a much better indication of relative strength. By that measure, the AL has had the NL’s number for quite a while:

NL Record vs. AL, 2003-2014
Season Won-Loss
2003 137-115
2004 125-127
2005 116-136
2006 98-154
2007 115-137
2008 103-149
2009 114-138
2010 118-134
2011 121-131
2012 110-142
2013 146-154
2014* 31-30
*Through the games on May 8

The last season the NL enjoyed a winning record against the junior circuit was 2003. Since then, the AL has won the regular season 10 straight years, by as few as two games and as many as 56 games.

We’re only a quarter of the way through the 2014 season, but the NL is on top, albeit by the slimmest of margins. So far, they’ve beaten their rival league in 31 of 61 contests.

Defense seems to have been a major factor in the NL’s resurgence. As recently as 2012, teams in the AL combined to handily outpace NL teams in Defensive Runs Saved. But last year and so far this year, the NL flipped the script and has more DRS than the AL.

Runs Saved by League and Season
Season AL Teams NL Teams
2011 39 -51
2012 185 -149
2013 -145 252
2014 -104 128

Through the games on May 8, the Angels (17 DRS), Royals (4 DRS), Red Sox (3 DRS) and Athletics (2 DRS) are the only four AL teams with positive Runs Saved totals. In contrast, all but four NL teams have positive DRS totals, and eight of the 15 teams in the division have at least 10 Runs Saved.


COMMENTS (13 Comments, most recent shown first)

3for3- Do you mean the first 2/3rds of the year? I'm sorry that I don't understand. I remember reading Mr. James going through meaningful games, and I wonder what the split would be for games that mean a lot. That being said, I reran the numbers using a single-df (one-sample) t-test. Just a simple stat test. You would expect NL Wins- AL Wins to be 0. Over 10 or so years, the average should be around 0. However, the average is close to -10, which differs significantly from zero by about 3 adjusted standard deviations. According to the numbers, you can be about 99% confident that the difference is NOT due to chance...
3:17 PM May 13th
This is just ignorant speculation, a great gift of mine. But since the difference is in defense, it it possible the DH factor works in reverse - that NL teams make position players of lousy fielding good hitting guys. Then in inter league game they don't offend those guys egos by making them DH. So their weakness is more in the field than at the plate?

5:00 PM May 12th
Bill is correct that a significant gap was closed by transferring the worst team from the worst league to the better league.

My quick study was here:
10:35 AM May 12th
Keen: I suspect if you used 2/3 year running totals, most if not all of them would show significance.​
9:27 AM May 12th
PS: does having your DH play his handful of games in the field for the year (e.g.: V-Mart, Papi) in these games have any discernible DRS diff?
8:15 AM May 12th
What is the current thinking on DH advantages? Any breakdowns on home and away records here?
8:11 AM May 12th
Welcome back, Bill. I bet that's right, too. It's a huge W-L differential that just got taken from the NL and added to the AL. And the Marlins are playing way better than they have been this year. Now, about those Cubbies...
9:54 PM May 11th
Moving the Astros to the American League did a great deal to balance out the quality of the leagues, I would guess. Worst team in baseball switches leagues, that probably moves 30, 40% of the difference between leagues.
1:54 PM May 11th
Could it be because of the DH ?.... nah.... no way... you don't say
1 professional hitter in the lineup the NL doesn't have... It can't be that... After all I'm just an idiot.
1:53 PM May 11th
Sgoldleaf... I ran chi-squares in each of the year. For the observed I used the posted games, the expected was a 50/50 chance as I think this is what you want to know, when is it significantly different than chance. 2006, 2008, and 2112 are significant years. 2112 is barely significant and if you use a Bonferroni correction it isn't. If you look at all the years combined, the Chi-square is around 15, and it is significant. Thus, statistically, there is something OTHER than chance overall, and in 3 of the years.
5:45 AM May 11th
Steven Goldleaf
I'd be interested in exactly when the difference became significant. I can easily imagine that there's a point that one league beating another is simply chance and a later point where it is definitely not chance, but I have no idea what the turning point would be.
9:41 PM May 10th
I'm long since reconciled to journalists and other pundits trying to discern long-term trends in the events of the last 25 minutes, but it's a bit disappointing when sabermetricians do it.
5:21 PM May 10th

Damn, John, life just sucks sometimes. Last night the Yanks beat the Brewers, the White Sox beat the Snakes, and the A's beat the Nats. The AL leads again, 33 to 31. Each divisions' W/L record in inter-league play so far (thru Friday night):
NL E 8-11
NL C 7-13
NL W 16-9
AL E 14-6
AL C 11-14
AL W 8-11
7:41 AM May 10th
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