The Strike Zone is (Still) Getting More Consistent

Not long ago, I pointed out a couple hilarious game strike zones called by Sean Barber and Clint Fagan. Both umpires called balls on pitches well within the usual zone, and both umpires called strikes on pitches somewhere around the shins. They were awful displays of umpire judgment, but after that, Barber called a much better zone in his next game, and far more importantly, both Barber and Fagan are Triple-A umpires and not regular major-league umpires. The regulars are better than the prospects, just like we see with the players.

And about those regulars — I’ve pointed out in the past that they seemed to be calling more consistent strike zones. One of the neat things about a post like that is that it can be updated, and now that we’ve got a few hundred games finished in 2014, I come bearing some further encouraging news.

I don’t intend to get into too much detail — the numbers can mostly speak for themselves. We’ll look at this in two ways. One leans on a homespun metric I’ve written about before that comes from the FanGraphs plate-discipline leaderboards. We know how many strikes and pitches there have been, league-wide. We know the rate of pitches in the PITCHf/x strike zone, and we know the rate of swings at pitches out of the PITCHf/x strike zone. What this allows for is a simple calculation of expected strikes, which can then be compared to the number of actual observed strikes. In the table below, you’ll see a couple meaningful columns. The first is the difference between actual strikes and expected strikes, per 1,000 called pitches. The second is the difference between actual strikes and expected strikes, per game.

Season	Diff/1000	Diff/G
2010	-31	-5.0
2011	-24	-3.8
2012	-16	-2.5
2013	-13	-2.1
2014	-5	-0.8

Per full game, five years ago, there were five fewer strikes than you’d expect based on the PITCHf/x strike zone. So far this year we’ve got a difference under 1, and the table shows a steady improvement. There are still fewer strikes than the automated zone wants there to be, but the gap now is practically nothing, relative to what it’s been.

Now, that doesn’t say enough on its own. What if umpires are calling way too many balls in the zone, and way too many strikes out of it? What if the mistakes are just balancing out? By the second approach, we’ll use data available at Matthew Carruth’s StatCorner. Carruth determines a strike zone as it’s actually called by the league-average umpire. Let’s look at the year-to-year rates of balls in the zone, and strikes out of the zone:

Year	zBall%	oStrike%
2010	15.2%	7.9%
2011	15.3%	7.3%
2012	14.5%	7.2%
2013	14.0%	6.9%
2014	12.9%	7.6%

In the early going, oStrike% has picked up a bit, perhaps because of an increased emphasis on catcher pitch-framing. Or perhaps because of something else. It’s a small increase, and it represents a return, for now, to a range it’s occupied before. Look over at the zBall% column. Umpires have called fewer balls in the zone than ever, and the improvement from last year, for now, is more than a full percentage point. I’m sure some of this is noise, because some of every sample is noise no matter how big, but we’re talking about a couple hundred baseball games. Just because it’s too early to say anything conclusively doesn’t mean it’s too early to be encouraged.

Even with the improvement, there are a lot of balls called in the zone, and there are a lot of strikes called outside of it. You’re never, ever, ever going to get strike-zone perfection, not as long as it’s up to people, particularly a lot of somewhat older people. But if you accept that there are going to be mistakes, you should be happy with any signs of improvement, and the strike zone now seems to be more consistent than ever. The best alternative to a perfect strike zone is a consistent strike zone, and though what we’re talking about is incremental, most of the umpires in the big leagues have been doing this for eons. It’s a little amazing they’ve collectively been able to make these adjustments, probably in part due to PITCHf/x feedback.

And there also might just be better catchers, who are better and thus more convincing receivers. Over the course of the season, we’ll monitor that oStrike%. But if better receiving makes for fewer balls called in the zone, it can’t be that much of a bad thing. Those who dream of an automated strike zone won’t find much to be happy about in this. One mistake might be one mistake too many. But home-plate umpires are evolving, and even if they never evolve into pitch-calling robots, this is far better than no growth at all.