Ian Desmond really should not play first base

When the Rockies signed Ian Desmond, the baseball world expressed its collective confusion. The Rockies aren’t bad exactly, but they’re not great either, and while I am almost always in favor of teams trying to win, they’re currently projected by FanGraphs for 78 wins — not exactly a team that just needs one more push to make the playoffs, and that’s with Desmond on the roster. And the move only got more confounding when the Rockies announced they intended to play him at first base.

It’s worth breaking down exactly why that plan seems so strange to those of us outside the Rockies organization. It’s not so much a question of whether Desmond can play first as it is a question of whether that’s the way to maximize his value. Desmond was a shortstop until 2015, then converted to center field in 2016, and while he didn’t have a sterling defensive reputation at either position, he was certainly passable at both; he almost definitely can play first base. So what’s so bad about sticking him there?

The positional adjustment is one of the backbones of WAR, an attempt to strip out the differences in value between players at two different positions. We know shortstop is harder than first base, and more valuable; what the positional adjustment assumes is that every average center fielder, shortstop, or fielder at another challenging position is an above-average first baseman or left fielder. That’s not true in every case, obviously, but it’s generally true, and it is one of the assumptions that makes WAR work.

Were that to apply for Desmond, there’d be nothing to worry about. If he’s an average center fielder, he’ll be an excellent first baseman, and his value to the Rockies will be the same at either position. But there’s reason to think that assumption is especially off-base in Desmond’s case.

First, a move from one extreme of the defensive spectrum to the other is most likely to break the assumptions. First base just has less opportunity to create value defensively than any other position. Anthony Rizzo is a really great first baseman, and his highest UZR in a single season is 8.3, in 2013. Billy Hamilton is a really great center fielder, and his highest UZR in a single season is 20.1, in 2014. Maybe Billy Hamilton would be a great first basemen, too, but to match the positional adjustment when moving from center to first, he’d have to have UZRs in the 30s, more than four times Rizzo’s highest UZR ever. It’s just harder to create defensive value at first base, even if you’re really talented.

Plus, there’s no reason to think a talented fielder at another position will maintain those talents at first. It’s easy to believe an average center fielder will be an above-average left or right fielder; the skills involved in the two are basically the same, and left and right field are still positions that are important defensively. Shortstop might involve different skills, but it’s more similar than different. First base, though, is totally different from every other position. It’s not so much that it requires more than any other position, but less. If a center fielder relies on his speed and good reads of fly balls to be of average value, those skills will go completely wasted at first base.

And, even among all players moving to first base, these caps on defensive value might apply more than usual to Desmond in particular. He played nearly 8,000 innings at shortstop, and over those innings, UZR graded him out just 8 runs below average, or about 1.3 runs per year. UZR for infielders can be broken down into three components: double plays, range, and errors. Desmond was fine on double plays (2.2 runs above average), and was good on range (16.4 runs above average). Where he struggled was on errors (-25.9 runs below average), as anyone who paid attention to his final season with the Nationals could tell you.

In other words, Desmond might have been a fine shortstop, but he was a fine shortstop because he could get to the tough ground balls that not every shortstop could get to. He was only a fine shortstop because he would occasionally do stuff like this:

One of those skills, the one Desmond is good at, translates not at all to first base; he won’t have many opportunities to go roving after grounders hit to holes. The other one, the one he’s bad at, is basically the most important part of playing first base! That’s not promising.

Since the signing happened, everyone has expected the Rockies to find some way to put Desmond in the outfield. It’s halfway through January; there’s still plenty of time. But the closer we get to Opening Day, the more likely it seems that they are genuinely going to stick him at the cold corner. They shouldn’t.