A straight platoon at first base isn’t a terrible idea for the Yankees

Entering the offseason, the Yankees’ first base situation stood out as one of the more tenuous areas of the roster. There existed uncertainty all across the diamond, of course, with a number of players hitting free agency, but no one knew quite what to expect when it came to the cold corner at Yankee Stadium. The Yankees, it seemed, could go in a number of directions, coming off a strange year in which Greg Bird forgot how to hit and Luke Voit forgot how to be Not Babe Ruth.

The Yankees have appeared to clear up that uncertainty by doing nothing. Sure, we could see someone like DJ LeMahieu take a turn at first base. Barring an unforeseen change, however, the Yankees will enter 2019 with Voit and Bird as their primary first basemen.

Earlier this week, Kunj Shah highlighted the problems the Yankees have had over the years at first base and how those issues may not get resolved this season. Now, let’s take a more optimistic assessment. If the Yankees committed to a strict platoon of Voit and Bird at first base, how good could that pairing be?

Voit and Bird make for a natural platoon situation. Bird, a prototypical lefty-swinging first baseman, could handle first base duities against right-handed pitchers, and Voit could take over against southpaws. Simple, straightforward.

Just how well could that easy split work out? We have a few ways to attack the problem. One might naturally think to look at each of their respective splits against pitcher of each handedness. That line of thought might fall through, however, due to the small sample sizes each player has put forth in their careers. Voit has recorded just 285 plate appearances, while Bird has 659 plate appearances to his name, despite feeling like he’s been part of the team for ages now. With such tiny samples to work with, it’s smarter to fall back on league-wide average platoon splits.

I enlisted Baseball Reference to generate our splits. They keep track of a metric called tOPS+. Essentially, tOPS+ takes a player’s (or, in this case, league’s) performance in a particular split and compares it to his overall performance, putting it on the OPS+ scale in which 100 is average. For example, if a certain player performed better in home games, his tOPS+ at home would be above 100.

In 2018, right-handed batters facing left-handed pitchers posted a 107 tOPS+. That means right-handed batters were seven-percent better overall when facing lefties. Left-handed batters facing right-handed pitchers posted 104 tOPS+, so they were four-percent better with the platoon advantage.

Let’s apply that split to the Yankees’ first base platoon, with some help from FanGraphs’ Steamer projections. At the moment, Steamer forecasts Bird for a .227/.315/.435 slash line and a 103 wRC+. The system is more bullish on Voit, projecting a .262/.335/.458 line and a 115 wRC+.

wRC+ works on the same 100-is-average scale as OPS+, so we’re probably safe to simply apply the same platoon advantages on that scale. This is a bit of a brute force method in which we’re doing just back-of-the-napkin calculations, but if Bird hit exclusively against right-handers and posted a wRC+ four-percent better than his true talent, we’d expect a 107 wRC+. Using the same simple math, we would expect a 123 wRC+ from Voit facing strictly left-handers.

We must also take into account the fact that MLB is populated with more right-handers than southpaws. In 2018, 59% of plate appearances involved a right-handed pitcher, leaving 41% for lefties. If we just force our expected wRC+ figures from Bird and Voit into that 59/41 split, we end up with a tidy 114 wRC+ forecast.

There’s also the matter of first base defense. DRS has rated Bird as seven runs below average in the field across over 1300 innings, while it has pegged Voit as five runs below average in under 500 innings. For simplicity’s sake, assuming Bird also plays 59% of innings in the field and extrapolating forward the pair’s historical DRS figures, we’d expect the two to combine for 10 runs below average in the field over the course of a full season.

In all, we’re left with a first base platoon that’s modestly above average at the plate, as the league-average wRC+ for first basemen has fluctuated from 105 last year, to 113 in 2017, and 108 in 2016. They would also check in as below average in the field. Put together, that profiles as essentially league-average production.

Does that sound about right? This was not a particularly nuanced approach to projecting the Yankees’ first base situation, but all things considered, average intuitively feels like a reasonable forecast. Bird was awful last year, but should regress positively in 2019. Voit was dynamite, but can’t possibly be expected to keep it up. The most likely outcome does appear to be a fairly middling first base platoon. Compared to the roller coaster of production the Yankees’ received at first base in recent years, steady mediocrity sounds downright quaint.