Strike Three?! Let’s Test in on Umpire Accuracy

About a yr in the past, I wrote about how umpires have improved at calling balls and strikes all through the pitch monitoring period. They have gotten a complete lot higher, particularly at figuring out strikes. While everybody appreciates a extra constant and correct zone, that has made issues a bit tougher for hitters total. More importantly, their progress didn’t look like it was displaying any indicators of slowing down. With the 2023 season within the books, it’s time to test in on whether or not that’s nonetheless the case. The methodology right here is straightforward: test to see if Statcast agrees with the umpire’s choice for every referred to as ball and strike. This isn’t an ideal technique, as a pitch proper over the guts of the plate is a a lot simpler name than one proper on the sting, however the monumental pattern sizes (there have been 376,635 takes in 2023) imply that issues even out over time.

First of all, total accuracy continued to rise in 2023. According to Statcast, 92.8% of takes have been referred to as accurately, up from 92.45% in 2022. In different phrases, umpires missed a name as soon as each 3.6 plate appearances. This isn’t terribly shocking, as accuracy has risen in each single season of the pitch monitoring period. Notably, within the final three years, the enhancements have been very practically an identical: 0.37%, 0.33%, and 0.35%:

This graph may make it seem like umpire accuracy isn’t in any hazard of plateauing simply but. It reveals three years of practically an identical enchancment and an total slope that’s roughly unchanged since 2008. However, issues look barely totally different if we break the takes down by whether or not or not they have been contained in the strike zone. It’s not essentially simpler to establish a ball accurately than it’s to establish a strike accurately. However, balls are straightforward to establish extra typically than strikes are, just because the realm exterior the strike zone is lots larger than the realm inside zone. In 2023, 55.5% of the takes on pitches contained in the strike zone have been additionally within the shadow zone. That is to say that when the appropriate name was a strike, it was normally a tough name. For takes on pitches exterior the zone, solely 31.3% have been additionally within the shadow zone. That’s a giant distinction! If you’ve ever tailored a cake recipe for a special dimension pan or heard a lecture concerning the relationship between quantity and floor space (or if you happen to’ve ever borne the brunt of Michael Baumann’s very sturdy opinions about what dimension pizza you must order), you probably know this intuitively. The strike zone is small and (in concept) vaguely rectangular. Outside the strike zone is, effectively, every thing else:

At the start of the pitch monitoring period, there was much more room for enchancment on pitches within the strike zone, and progress there got here extra quickly. That is not the case. Umpires are nonetheless enhancing at roughly the identical sluggish, regular tempo on pitches exterior the zone. However, contained in the zone, their accuracy has truly declined by a hair over the previous two years. In different phrases, it seems like we’re lastly studying the bounds of umpire accuracy, at the least on pitches contained in the zone:

Last yr, I broke issues down by Baseball Savant’s assault zones. This time, I’m going to focus solely on the shadow zone, as a result of umpires have gotten so good on the different zones that there merely isn’t a lot room left for enchancment. Over the guts of the plate, they obtained 99.26% of calls proper in 2023, down only a hair from 2022. In the chase zone, they have been at 99.24%, up a hair from 2022. Neither change was greater than seven-hundredths of a p.c, and neither has deviated by a lot as half a proportion level in whole over the previous 5 years.

In the waste zone, umpires missed simply two calls all season. As you may need guessed, these weren’t regular pitches. Both missed calls got here on significantly eephus-y eephuses from place participant Ryan McKenna:

I feel we are able to forgive Jordan Baker for letting Adley Rutschman persuade him that these two parabolas have been truly strikes within the ninth inning of a 12-2 recreation.

Between the chase, waste, and coronary heart zones, we’re speaking about simply 1,301 missed calls whole in 2023. That’s 1.87 misses per recreation. I don’t know what threshold for error different folks may need, however I can’t actually think about asking umpires to enhance far more than that.

More importantly, that implies that any modifications are taking place across the edges of the plate, within the shadow zone. Keep in thoughts that roughly 42% of all pitches are within the shadow zone, and roughly 80% of all takes. At the start of the pitch monitoring period, that quantity was down under 76%, however as umpires improved, each pitchers and hitters obtained a greater sense of the zone. Now greater than ever, that is the place the motion is:

Although the general slopes are very clear, the traces on this graph are much more jagged, which is sensible. These are all shut calls! Back in 2008, umpires obtained them proper lower than two-thirds of the time. Now they get them proper 81.9% of the time, effectively over four-fifths. That implies that umpires are lacking roughly 9 calls within the shadow zone per recreation. From 2022 to 2023, total accuracy within the shadow zone improved by 0.92%, and it has improved at a median of 0.89% for the final three years. In that sense, the advance reveals no indicators of slowing down.

That stated, check out the blue line. It makes a fairly compelling argument that umpires have reached their restrict on accuracy, at the least for shadow zone pitches contained in the strike zone. Over the final 4 seasons, the accuracy has stayed between 81.33% and 81.87%. That’s a complete deviation of simply 0.54%. It’s the primary time we’ve ever seen that form of stability within the entirety of the pitch monitoring period, so it might be a shock to see the accuracy instantly begin climbing once more. Maybe that is pretty much as good because it will get.

However, on shadow zone pitches which can be exterior the zone, umpires are nonetheless enhancing. In truth, accuracy exterior the zone has improved by greater than 5% over the past 4 seasons, and by at the least 1.25% in every of the final three seasons. It has surpassed accuracy contained in the zone for the primary time since 2016. There’s no signal of a plateau right here, which leads me to consider that the purple line might carry on going up. Still, I can’t think about there’s that a lot room for enchancment, seeing as accuracy on pitches contained in the zone simply hit its peak proper across the similar spot.

Whereas final yr I got here away from my analysis pondering that the improved accuracy in ball-strike calls confirmed no indicators of slowing down, I’m beginning to lean the opposite manner. The margin for enchancment is already vanishingly small, and one of many key drivers of the enhancements — shadow zone pitches contained in the strike zone — looks as if it has plateaued. Moreover, we all know that umpiring is getting tougher. Pitches are getting sooner and shifting extra, and there are extra calls than ever on shadow zone pitches that might go both manner. In 2023, umpires missed just below 11 calls per recreation, and 9 of them have been within the shadow zone. As lengthy as that purple line retains shifting upwards, there’s room for at the least a little bit enchancment, however I’m beginning to suspect that it gained’t be going up for very for much longer.