Is MLB Already Shrinking the Strike Zone?

Some background: Last May, baseball floated the ideas of eliminating the four-pitch intentional walk, and also raising the strike zone’s lower boundary. This past February, there was a formal proposal. Everything was subject to the union’s agreement, and as you know, the union signed off on the intentional-walk part. But it didn’t agree to other stuff, including the strike-zone change. Although MLB is free to implement changes unilaterally, that can’t happen for a year after initially giving notice.

You’d think, then, that the strike zone is safe, for now. That nothing should look very different in the nearer-term future. After all, that’s how the agreement is supposed to work. But what if that isn’t how the agreement is working? Brace yourself as I make too much of what’s entirely too little data.

If you’ve been paying attention to the strike zone at all, and if you’ve been doing it for years, you know that the zone has consistently gotten lower and lower, and therefore bigger and bigger. Maybe it’s been a consequence of having PITCHf/x, maybe it’s been a consequence of better pitch-framing; whatever the case, what’s happened has happened. Here’s a very simple way to visualize things. Making use of Baseball Savant, I examined the lower third of the strike zone. Here are regular-season rates of called strikes, out of all called pitches in the area:

The plot begins with a low of 65%, in the first year of widespread, publicly-available pitch-tracking information. Then you see as the line shoots up, having recently brushed up against 90%. Catchers have been setting low targets. Pitchers have been hitting low targets. Umpires have helped out by granting those pitches more and more.

None of that is controversial, or even possible to question. It’s all fact. Now let’s turn to spring-training data! I have to warn you we do not have very much of this. There’s tracking in only a small number of ballparks, so you need to take this with a grain of salt. I’m taking it with a grain of salt, and I’m writing the damned thing. Here is the same kind of plot as above:

The same general trend can be observed. More and more strikes have been granted in or around the lower third of the “expected” strike zone. The most interesting bit is all the way to the right. Compared to last spring, this spring’s rate is down a hair over five percentage points. Obviously, no such decline has been observed before, within the limited window. What it means: If there are fewer called strikes in the bottom of the zone, the lower boundary has effectively been lifted. Not by very much, not to a degree where the entire game of baseball would be different, but changes are changes.

Again, and this is important, we’re going to need more information. We’ll get that information within the next month. The regular season will immediately provide plenty more data, with pitches by the thousands, and then we’ll be able to see where we are. This is just a possible hint, a first whisper of a subtle change to the game. It wouldn’t be something happening randomly; the league already said it would like to raise the lower border. The union didn’t sign off, yet the league is ultimately in charge of how it operates.

In fact, you could argue change began last year. Consider this article from October by Jon Roegele, titled “The 2016 Strike Zone.” I’ll quote:

After six consecutive seasons in which the strike zone size increased, both in general and in particular at the bottom of the zone, the zone tightened ever so slightly this year.

Emphasis on “ever so slightly” — by Roegele’s measurements, the overall zone got smaller between 2015 and 2016 by less than 1%. There was a small reduction in called strikes granted around the bottom. It was interesting to see the growing zone plateau, the growth even slightly reversing, with the commissioner starting to talk about the zone as a priority. It might be no accident the zone didn’t get any bigger. Now there’s limited evidence the zone could be in for shrinking further. We’ll see if it holds up, as information pours in, but finding a potential explanation wouldn’t require much work.

It’s not something that would necessarily be unfair. It would be no more unfair than the expansion of the strike zone in the first place, which has worked to the detriment of the hitters. The game’s already been changing, and even shrinking the zone might just take things back to where they were in, say, 2014, or 2012. The players say they don’t want to agree to a fundamental change, yet there have already been fundamental changes, for reasons found nowhere in the rule book.

It’s just, this is something to keep an eye on, because the MLBPA already declared it prefers the zone to stay the same. The zone doesn’t have a recent history of staying the same, and there’s reason to believe some of the recent expansion could be in the process of being reversed. We’ll know more pretty shortly, but, what is spring-training data for, if not to provide possible clues of the future?