Thursday, February 28, 2013
Chat leftovers: Evaluating defense
By David Schoenfield
I promised a follow-up to the following question from Tuesday's chat (question edited for clarity):
Jack (Toronto): Continuing the Defensive Runs Saved discussion, don't you end up punishing players for teams that have high strikeouts, or infielders if their pitchers give up a lot of flyballs, or outfielders if a lot of groundballs? They would obviously get less chances for DRS.
Not wanting to mess up the answer, I reached out to Ben Jedlovec of Baseball Info Solutions, the company that computes Defensive Runs Saved. Ben is the co-author of "The Fielding Bible Volume III," which I highly recommend if you're interested in digging deeper into how fielding is evaluated. Here's Ben's response:
Defensive Runs Saved (DRS) evaluates each fielder's performance based only the opportunities presented to them. How many runs did that fielder save (or cost) his team compared to an average fielder under the same circumstances? That's Defensive Runs Saved.
Let's take an extreme example to illustrate the point. Imagine a shortstop behind a pitching staff that allows only outfield flyballs. He's going to have zero opportunities to make any plays, so he's going to wind up with 0 Defensive Runs Saved -- exactly average. He might be above average or below average, but we don't know, since he never had a chance to show us.
Imagine that shortstop instead played behind a ground balls-only staff. We're going to have plenty of chances to evaluate his defense. If he's above average at the position, he could very well end up with a higher Defensive Runs Saved total than he would have under ordinary circumstances. If he's below average, he could prove more costly in the field than he would have behind a more typical staff.
However, a difference in the number of opportunities alone is not going to give an above-average defender a below-zero DRS, or vice-versa.
Hope this helps!
Makes sense, doesn't it? It's no different than the same hitter getting 600 at-bats versus 500 at-bats: He's going to be more valuable the more chances he gets to hit. It's not a form of punishment but rather a form of opportunity cost.
In the chat, I mentioned the Braves' outfield trio of Michael Bourn, Jason Heyward and Martin Prado, all of whom put up excellent defensive metrics in 2012. As it turns out, the Braves' staff was not a flyball-heavy group; in fact, the Braves allowed the fifth-highest groundball percentage in the majors. Those three were just really good last year.