The Strike Zone Has Gotten Smaller

Some while ago, baseball sent a packet to the player’s union, and within a few ideas were reportedly mentioned that might potentially help restore what had been dwindling levels of offense. There was talk about maybe lowering the mound. There was talk about the DH. There was talk about livening up the baseball, and there was talk about tweaking the strike zone. There was other stuff, too. It was probably a detailed packet.

Now, those were just scattered ideas, conversational starting points. Nothing was made into rule, but it’s interesting to reflect on the point about the ball, given recent research by Ben Lindbergh and Rob Arthur. Or, if you prefer, just given recent home-run trends. Rob Manfred has denied that anything about the baseball has changed, but balls have gone flying and run-scoring is up. It is, at the very least, curious. Not that fans are complaining.

And then there’s the matter of the zone. Manfred correctly observed that the zone had expanded. It’s possible that, as soon as next season, the strike zone could be officially raised. Major League Baseball has stayed on top of the research, and league officials understand that the zone grew over time, in particular around the knees. Next year, we could have a rule change. But based on indications, we’ve already seen the strike zone move a little up. For the first time in recent recorded history, baseball is using a strike zone smaller than the one it had the year before.

Jon Roegele is the best at this stuff, and he’s way better at generating nifty strike-zone graphics. Compared to him, I’m terrible, but thankfully FanGraphs already automatically creates data displays like these. So let’s start there, looking at league-average called-strike-rate plots for each of the last two seasons. It’s 2015 on the left, and it’s 2016 on the right, and these are from the catcher’s perspective. I know the numbers are small, but, you can squint. I know you’re capable of squinting.

There’s nothing that’s dramatically different. We all would’ve noticed a strike zone that was dramatically different, since the zone is so central to the gameplay. For the most part, things have been consistent, but look for the little changes. There’s a drop of a point low and to the left. A drop of a point low and in the middle. A drop of two points low and to the right. More drops of a point below the zone. No other zones have compensated for those drops. There have, simply, been fewer low strikes.

Here’s a different sort of display, now showing information stretching back to 2008. I’ve named six of the zones above. I’ve focused on the lower three boxes in the zone, and the upper three boxes in the zone, numbering them 1, 2, and 3 from left to right. Let’s look at how the called-strike rates have changed.

It couldn’t be easier to spot the lower zone expansion. For the most part, the upper areas have remained fairly consistent. There have been some slight drops, as more and more catchers have set up low. Pitchers have targeted low, and the zone has cooperated. If you follow the Low 1 box, you see a steady increase, until 2016. If you follow the Low 2 box, it’s the same story. And the Low 3 box is also the same story, excepting that weird little dip in 2009. The zone got lower, and lower, and lower still. It’s still quite low, relative to where it was at the beginning of the PITCHf/x era, but it looks like the trend has been stopped, and even partially reversed. The zone looks more like it did in 2014, instead of 2015 or worse. It’s something.

If you want a little more detail, those same FanGraphs displays offer the opportunity. These plots are the same as the plots above, except the numbers are broken down into more areas. Again, 2015 on the left, 2016 on the right:

The biggest movement is low. It’s still subtle, and nothing you’d notice in any given individual game, but the numbers are the numbers and the samples aren’t so small anymore. To keep breaking it down, here are the plots for right-handed hitters:

You see dips low, and mostly low and away. For left-handed hitters:

It’s the same, but reversed. Fewer called strikes low, and in particular low and away. That works to a hitter’s benefit: The most difficult area to hit is low and away, so when those pitches are called balls instead of strikes, the hitter gets a breather and another opportunity for something to smash. If you think about it, as we consider reasons for why offense is up, it seems like it’s mostly about the home run. And that focuses attention on the baseball itself. But the different strike zone probably hasn’t not helped. It would be a little factor, but it’s something.

It’s hard to know exactly how to explain this, but fortunately, my job doesn’t depend on that. And Lindbergh and Arthur (and Roegele!) are the exhaustive researchers, not me. I’m more of the observational type, and what I’m observing is that the strike zone has gotten a little smaller this season, mostly because of pitches down. That’s notable because we hadn’t seen the zone get smaller before. It breaks what had been a powerful trend. Maybe the game is working with slightly different umpiring crews, drawing more from Triple-A. Maybe catchers, for some reason, are setting higher targets. Most probably, this is a response to the sinking zone getting so much attention. With all the talk about raising the lower boundary, it only makes sense that could worm its way into umpiring minds. Next year, we could have an official strike-zone rule change. This year, we’re getting a bit of a sneak preview.