The motivation for this research comes from the excellent article “Best Outfield Arms of 2008,” by John Walsh of The Hardball Times. What we often forget, or fail to recognize, are the occasions when runners stop dead in their tracks when they realize who is fielding the ball. These are the moments that outfielders never get enough credit for. Let’s not evaluate outfield arms solely by looking at how many assists they have from a year-to-year basis. What we should focus on is which outfielders prevent opposing runners from putting their team in a better position to score runs.
The assumption is that outfielders prevent runners from taking extra bases solely with their arm strength. We often ignore the similar effect of a quick release, impressive range, or most efficient route to the ball. Quantifying this is the tricky part. If you don’t have a play-by-play breakdown of every game which also tells you where the runners are before and after the play, then you may be out of luck. Fortunately, Bloomberg Sports has access to such data.
The four situations in which we typically see a runner taking an extra base are:
1. Going from 1st to 3rd on a single with 2nd base unoccupied
2. Going from 2nd to Home on a single with 3rd base unoccupied
3. Going from 1st to Home on a double with 2nd base unoccupied
4. Going from 3rd to Home on a flyball with less than 2 outs.
While #4 is obvious, I’ve added the prerequisite for 1-3 that the base in front of the runner be unoccupied as well because it is difficult to assume whether or not the runner is holding up because of the runner in front of him or because of the outfielder’s arm.
There are two ways to analyze these situations. We can look at the rate of how often runners take the extra base against the outfielder, or we can take a more complicated route that may need greater explanation.
Essentially, the team at bat is expected to score a certain amount of runs based on outs and base runners. An example based on results from 2012, with runners on 1st and 3rd and 0 outs, the batting team is expected to score 1.789 runs that inning. That number comes from looking at how many times this situation occurred and then finding the average number of runs that scored in that inning after that situation. So for evaluating outfielders, we will look at the run expectancy before the event, find out what the run expectancy should be after the at bat, and compare it to what the run expectancy is after the at bat.
Please note, I have grouped the results by position because base runners are far less likely to try to take 3rd on a single if the ball is hit to left-field. Here are the best outfielders at preventing runners from taking extra bases.
Best Right-Fielders: Extra Base Taken%
Best Right-Fielders: Runs Allowed per Opportunity
While some of these names are not surprising (Francoeur, Bautista, Ichiro), I did not expect Ben Revere or Ben Zobrist to crack the list. Zobrist and Revere do have a reputation as good outfielders, though neither of them are known for their arms. What this does show is that Francoeur’s reputation as a sterling defensive right-fielder is well deserved.
Best Center-Fielders: Extra Base Taken%
Best Center-Fielders: Runs Allowed per Opportunity
The Angels get a lot of grief for playing Bourjos in center and Trout in left, but it appears they may know what they’re doing. Bourjos ranks first in both methods and by a wide margin. Matt Kemp and Colby Rasmus also make appearances in the top five.
Best Left-Fielders: Extra Base Taken%
Best Left-Fielders: Runs Allowed per Opportunity
You probably didn’t expect to see Ludwick make the cut, but he contributed in the field as well as at the plate. Prado, Jennings, and Cespedes were also among the top defensive stars (Mike Trout did not have enough opportunities to qualify).
It is important to note that there will be a great deal of variance from year to year as sample sizes are somewhat small and not all singles, doubles, and fly balls are going to be hit the same way to each outfielder. It is also important to note that we are not evaluating who has the best arm, but who is the best at preventing runners from improving their team’s chances to score. I assure you that if we were evaluating who has the best arm, Ben Revere would not show up on this list.
Tomorrow we will shift our focus to outfielders who are the worst at preventing runners from taking the extra base.