What’s going on with Aaron Judge’s Yankee Stadium splits?

If Baseball God, in all its terror and TOOTBLAN, came down from on high and told you your team could have peak Barry Bonds for half the games he plays, and then current Albert Pujols for the other half of the games, would you accept that deal?

If you’re a Yankee fan, you might already have! This is basically what Aaron Judge has been, when you look at how he plays on the road versus how he does at home. In the Bronx in 2018, Judge posted a ludicrous 210 wRC+, and that drops all the way down to 90 on the road. At a time when home/road splits are discussed fervently, from Manny Machado to DL LeMahieu, it’s worth taking a closer look at the best player on the Yankees and find out what the heck is going on.

Let’s start with where I almost always start in analysis these days, Statcast. Aaron Judge makes arguably the highest-quality contact of any hitter in baseball, ranking in the top two of both average and max exit velocity in both of his full MLB seasons. If his drop in production was driven by hitting the ball poorly away from Yankee Stadium, Statcast would give us the clues.

There really isn’t any difference in his raw data at home or away, though. His average exit velocity is less than half a mile per hour different between the splits, and he actually hits the ball on a lower trajectory at home:

than on the road:

Meaning, we should expect a little better production on the road, all else equal. But, of course, something isn’t equal. The real difference is Judge’s strikeouts and walks.

In the Bronx, Judge walks about 18% of the time, and posts a BB/K ratio of 0.87, which would be good for eighth-best in all of baseball if he did it full-time. Away from home, though, that rate drops all the way down to 0.37. Basically, at home Judge has Mookie Betts-levels of zone command, and on the road he mirrors Starlin Castro.

Unfortunately plate discipline splits aren’t super easy to find, in terms of actual swing and miss rates. What I wonder is, how much of Judge’s apparent discipline problems are his own and how much is the fault of the umpire?

Travis Sawchik, among others, have written about how poorly Judge’s personal strike zone is called. We also know that umpires call pitches out of the zone strikes about 4% more often against the away team. What I’m wondering is how much that affects Judge’s discipline, and whether there’s a trickle down affect.

Working with an inconsistent strike zone affects all parts of your hitting, since it changes the pitches you can swing at, and forces you to protect more at the plate, rather than just swinging away. If Judge is working with a strike zone that’s hard to follow, it’s not that far of a leap to suggest it’s why he struggles so much on the road.