In my book, The Fielding Bible, we came up with a way to evaluate outfielder arms. We look at two elements: Runner Advance Percentage -- how often do runners succeed at taken an extra base on a single or double, and Baserunner Kills -- how often does an outfielder directly throw out a runner at a base (no relays). Based on these two statistics, here's how we evaluate players in the first half this year.
Starting in left field, the player with the most kills so far this year is Raul Ibanez with five. Also with five kills out of left field are Delmon Young and Ben Francisco. Ibanez has allowed only 35.8 percent of baserunners to take an extra base, which is above average for left field. However, Pat Burrell, while he has only four kills, has only allowed 29.9 percent of baserunners to advance. Based on his better advance percentage, we select Pat Burrell as the left fielder with the best throwing arm in baseball so far this year.
In center field we have former second baseman B.J. Upton with eight kills thus far. That ties him with right fielder Nick Markakis for the most baserunner kills in baseball. However, Upton’s 71.4 percent advance percentage is one of the worst among all center fielders. The best throwing center fielder for 2008 might come as no surprise. It’s former pitcher Rick Ankiel, who along with four kills, has only allowed 47.1 percent of baserunners to advance, the best figure among center fielders with 40 or more opportunities.
In right field, we already mentioned Nick Markakis with eight kills, but somewhat similar to B.J. Upton, his advance percentage of 54.7 percent is below average. The best throwing right fielders in baseball this year are Hunter Pence and Michael Cuddyer, each with five kills and each with a 46.3 advance percentage. They’re tied for second in best advance percentage among all right fielders. Kosuke Fukudome leads the way with a 45.2 percent advance percentage but only two kills.
In summary, here are the best so far this year:
| | | Baserunner | Advance | League Average |
| Position | Player | Kills | Percentage | Advance Percentage |
| | | | | |
| Left Field | Pat Burrell | 4 | 29.9 | 41.8 |
| | | | | |
| Center Field | Rick Ankiel | 5 | 47.1 | 58.2 |
| | | | | |
| Right Field | Hunter Pence | 5 | 46.3 | 53.3 |
| | Michael Cuddyer | 5 | 46.3 | |
Source: BillJamesOnline.com (through the All-Star break)