The Strike Zone Is Changing

Even though the existence of this piece is based on opinions relayed to me by multiple players, none of those players’ actual name appear within it. Why? Because nobody wants to go on record about the strike zone. They do have feelings about that zone, though. Especially lefties. And there’s evidence that the lefty strike zone is changing.

One lefty slugger was recently telling me about his approach and then made sure that we were off the record to throw in an aside: “… because they’re calling the lefty zone more true on the inside these days.” A catcher was adamant that he’d heard from umpire crew chiefs that there was an added emphasis on those pitches in to lefties. Another catcher echoed the sentiment and added that umpires were looking harder at the bottom of the zone. One lefty hitter called it garbage. A third catcher just shook his head at the whole thing.

Though none of these players would put their name to the complaint — fair, since they have to interact with the umpires going forward and wouldn’t want to poison that conversation and put a bullseye on their backs — there was enough smoke here to investigate the situation for fire.

We know the official line from baseball itself. Though Commissioner Rob Manfred is on record saying that he would like to consider a change to the strike zone, he’s also on record as saying any possible changes will be pushed to 2018. That’s weird, though, because we already witnessed a change to how the lower part of the strike zone was being called in spring. That change did not make it to the regular season, where the ratio of balls to called strikes in the bottom four inches of the zone has stayed steady compared to recent norms.

That doesn’t mean that the zone isn’t changing. It’s just that lefties are the only ones seeing the change.

The zone has long been shifted to the outside part of the plate against lefties, to the point where I’ve usually added a couple inches to the outside and taken them off the inside when I’ve done zone queries that include left handers. Hyun Soo Kim mentioned that umpires here call the inside pitch to lefties less often than they did in Asia. Jon Roegele (of course) delved in deep into the lefty strike zone if you want to know more.

But that was in 2013. Today’s lefty zone looks different. Look at the inside part of the plate on these excellent heat maps from my colleague Sean Dolinar. Notice how the inside part of the plate in 2017 is more yellow than it was at the same date in 2015, and the outside part of the plate a little more blue now than it was before. (These are from the catcher’s perspective.)

Maybe you don’t like squinting at colors. Here’s the ratio of balls to called strikes on the inside part of the plate. This time, I defined the zone by the rule book and added four inches towards the heart of the plate, so +0.7 to +1.0 on the heat maps above.

Umpires are calling more strikes to lefties on the inside part of the plate. More than they ever have since we’ve been able to track this. As much as 40% more often compared to historic levels. Turns out, some of those disgruntled lefties were right.