The Problem With Position Adjusted Stats

This came up in the Coco Crisp trade thread yesterday afternoon, but I felt like it’s worth a larger mention. It’s one of the things that I see repeated frequently among fans and analysts alike, but it just lacks the validity of it’s claim. I’m referring to the notion that a player who is moved from an up the middle defensive position to a corner defensive position loses a significant amount of value – you’ve probably seen this stated as something like the following:

“David DeJesus is a very good center fielder, but his bat makes him just an average left fielder.”

These kinds of statements are mostly due, in my opinion, to the rise of metrics that compare players against an offensive baseline of other players who play the same position. Since the average hitting LF is significantly better than the average hitting CF, moving a player from CF to LF will make him look quite a bit worse. He’s now getting compared to a better crop of players, so his relative ranking falls.

The problem, however, is that the relative drop in offensive value is almost entirely offset by a relative increase in defensive value.

Let’s look at LF/CF, for instance. Last year, major league left fielders hit .269/.344/.442, while major league center fielders hit .268/.334/.420. Over a full season, the offensive difference between a corner OF and a CF equals about 12-14 runs. Over that same full season, the defensive difference between a corner OF and a CF equals about 9-10 runs.

The net difference in moving a quality defensive CF to a corner OF spot will be a loss of somewhere between 2-5 runs, thanks to the decreased amount of opportunities that CF will get playing in a corner. Of course, if you replace that CF with another CF who is significantly better with the glove, you can get those runs right back by getting the premium defender more opportunities.

We really need to get over this idea that guys like David DeJesus, Carl Crawford, and Ichiro Suzuki lose a significant amount of their value because they’re not playing center field. The difference in their value in CF vs a corner is pretty small, and there are many cases where it certainly makes sense to have a premium defender in an outfield corner.

We have to get away from this notion that a good defender is wasted in a corner. It’s just not true.