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Playoff Umps Are Screwing Up A Tenth Of Balls And Strikes

Nothing preoccupies players, managers and fans during the postseason like an umpire’s strike-zone judgment. While there’s plenty of outcry over balls and strikes in the regular season too, the stakes are much higher — and the complaints correspondingly louder — when an entire championship can hang on one errant call.

But although this year’s playoffs have contained a couple of poorly called games, it’s not quite time to kill the umpires yet. Their overall strike-zone accuracy this postseason has not been significantly lower than what it was in the regular season, nor has it been much worse than you’d expect if you picked a handful of MLB games at random.

Take, for instance, the Chicago Cubs’ NL Division Series Game 1 loss to the St. Louis Cardinals, in which both fans and players found fault with an inconsistent strike zone. During that game, home plate umpire Phil Cuzzi missed 15 ball-strike calls, for a total accuracy rate of 88.4 percent.1 That’s bad — it ranks among the worst 10 percent of all MLB games this season — but consider as well that 10 postseason games have been played so far.2 In a sample of that size, the probability that we wouldn’t see a game called as poorly as the Cubs-Cardinals series opener was only about 34.9 percent,3 so the odds were good that some team was going to be on the receiving end of a bunch of bad calls. The Cubs simply had the misfortune of being that team.

Despite that bad game, there’s nothing statistically unusual about this postseason’s umpiring performance. In the playoffs as of Oct. 10, the umps have an accuracy rate of 91.4 percent. Depending on how you feel about robot umps, that kind of accuracy may seem unacceptable, but it’s right in line with the season-long MLB average of 91.6 percent. And if you randomly chose a set of 10 games from the regular season, you’d find that the umpires were less accurate than they’ve been this postseason about 36 percent of the time.

Because MLB bases its postseason crew assignments on merit, we might expect the playoff umpires to have a better accuracy rate than the overall regular-season average. But as my Grantland colleague Ben Lindbergh noted last year, since 2009 there’s been essentially no difference in strike-zone accuracy between regular-season and postseason games.4 So although it would be nice if the strike zone were being called more precisely in the playoffs, the umpires’ execution so far is almost exactly what we’d expect based on their performance during the regular season.

Footnotes

  1. To measure an umpire’s accuracy, I built a model of the strike zone that takes into account not only the physical coordinates of the pitch, but also the count and the framing ability of the catcher, factors that are important determinants of the zone’s dimensions.

  2. This article includes data only through Oct. 10.

  3. The probability that all 10 games would rank among the best 90 percent of MLB games is 0.9 raised to the tenth power, or 0.349.

  4. If anything, the postseason umpires have been slightly less accurate.

Rob Arthur is FiveThirtyEight’s baseball columnist and also writes about crime.

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