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Prophetic Umpires: Expectation Bias and Errors in Baseball

It’s not that what you see is what you get. It’s that what you expect is what you see.
(Photo: Will Hughes/Shutterstock)

(Photo: Will Hughes/Shutterstock)

“It ain’t nothin’ till I call it,” said umpire Bill Klem. And if he called it a strike, a strike it was. As Klem knew, the umpire has something resembling papal infallibility. That was then. Klem worked behind the plate from 1905 to 1942 and holds the record for throwing players and managers out of the game (the infallibility thing is sometimes a bit much for players to take). Now, thanks to modern technology, we can know just which calls the umpires miss.

Here’s Matt Holliday. It’s strike three and it was three bad calls.


Holliday’s body language speaks clearly, and his reaction is understandable. The pitch was wide, even wider than the first two pitches, both of which the umpire miscalled as strikes. Here’s the data:


The PITCHf/x technology that makes this graphic possible, whatever its value or threat to umpires, has been a boon for sabremetricians and social scientists. The big data provided can tell us not just the number of bad calls but the factors that make a bad call more or less likely.

In the New York Times, Brayden King and Jerry Kim report on their study of roughly 780,000 pitches in the 2008-09 season. Umpires erred on about one in every seven pitches—47,000 pitches over the plate that were called balls, and nearly 69,000 like those three to Matt Holliday.

Here are some of the other findings that King and Kim report in the recent article.

  •  Umpires gave a slight edge to the home team pitchers, calling 13.3 percent of their pitches outside the zone as strikes. Visitors got 12.6 percent.
  • The count mattered: At 0-0, the error rate was 14.7 percent, at 3-0, 18.6 percent of pitches outside the zone were called as strikes, and at 0-2, only 7.3 percent of pitches outside the zone were called as strikes.
  • All-Star pitchers were more likely than others to get favorable calls...
  • ...especially if the pitcher had a reputation as a location pitcher.
  • The importance of the situation (tie game, bottom of the ninth) made no difference in bad calls.

It seems that expectation accounts for a lot of these findings. It’s not that what you see is what you get. It’s that what you expect is what you see. We expect good All-Star pitchers to throw more accurately. We also expect that a pitcher who is way ahead in the count will throw a waste pitch and that on the 3-0, he’ll put it over the plate. My guess is that umpires share these expectations. The difference is that the umps can turn their expectations into self-fulfilling prophecies.

This post originally appeared on Sociological Images, a Pacific Standard partner site, as “Umpires and Expectation Bias.”