Double Plus: On David Peralta, Yasmany Tomas Swapping Positions

If you were ever relegated to right field in little league, you might not think of it as a premium skill position. Still, the number of left-handed hitters in the majors neutralizes the difference in fielded balls between right and left. Last year, right fielders made 9,416 plays for outs, and left fielders 8,644. That’s about 9% more plays, and that doesn’t necessarily take into account all balls fielded (the non-outs can still affect runner advancement), but you get the idea: it’s not like right field is less important than left.

Right field is also different from left, because the game isn’t symmetrical; runners run counterclockwise. Outfielders rarely get the ball in time to affect a play at first base (and when they do, it can be because only right field is close enough — just ask Gerardo Parra). A left fielder trying to get the ball to first to beat a runner that has a long way to tag up does happen, but nowhere near as often as it becomes important for a right fielder to try to prevent a runner from taking third.

A week ago, Chip Hale told Nick Piecoro that the D-backs were considering a switch of David Peralta and Yasmany Tomas in the outfield, with Peralta moving to right and Tomas to left. Why?

You should read the whole Piecoro piece, but it seems like it’s partly because right field has begun to be thought of as a skill position (at least it seemed that way two years ago). Maybe left field really is less important, and Peralta is the better defender, and it’s as simple as that. In the Piecoro piece, he indicates that Tomas played in right last year because that’s where Tomas said he was most comfortable, presumably between the two corner outfield positions.

This is a time in which numbers can’t do us a whole lot of good; evaluation of the two players in other ways and understanding the mechanics of the game are all we have. A player’s comfort level probably does matter quite a lot. It’s a bit of a strange coincidence, since last year Mark Trumbo was moved from left to right in part because that put his glove closer to the foul pole; when I did a little study with all outfielders with at least 1,500 innings in both spots between 2003 and 2014, I found that that might be a slight advantage.

What stuck out most, though, was how right-handed outfielders more or less broke even, but that left-handed outfielders did not. Following that Trumbo Rule, you’d prefer to have a lefty like Peralta in left field, with his glove on his right hand, closest to the pole. The lefties in my very small sample in that study did quite a lot better in left — 5.5 runs per 150 games better on defense, which more than half a win, and pretty enormous. I’m not sure how likely this really is as A Thing, but it’s worth noting that the D-backs shifted the outfield around just for Trumbo one year ago, and are now considering a shift of two guys that would ignore that same principle. I’m not sure that’s a bad thing.

It seems like Peralta probably is the better fit in right field. It’s not always the most direct route, but Peralta can get there, and seems to have Tomas beat in foot speed. In terms of range, Peralta probably has the advantage, and all we know from the numbers is that we probably do want more range in right. Since right fielders are only compared to themselves, the numbers also don’t get us too far with throwing arm; and yet we can safely know that right fielders probably affect the game more with their throwing arms than left fielders. The D-backs had a former lefty pitcher put up one of the finest defensive seasons on record at any position in 2013; I definitely buy that Peralta’s left arm is stronger and more accurate than the right arm of Tomas.

If the D-backs go through with this, we may not notice too much of a difference; the fact that quite a few teams hide offense-slanted players in left could also make Tomas look quite a bit better on paper. The change could also be motivated by other outfielders; Peralta’s days-off matches might be better fits right field (say, Socrates Brito). It doesn’t seem like it could really hurt, anyway, and maybe it would be better than that.

We don’t have a large enough sample of playing time for Peralta in different spots, but it also seems worth noting that Gerardo Parra has played between 2 and 3 seasons’ worth of innings in both corners, and has been dramatically better in right (13.4 UZR/150 for his career in right, 8.6 UZR/150 in left). Peralta isn’t the same person, but maybe he can do the same thing.