MLB umpires have a different strike zone in extra innings

A nine-year study reveals MLB umpires favor the leading team on ball-strike calls in extra-inning games.

We’ve all been to MLB games that went into extra innings. In some of these games, the visiting team scores in the top of the inning. With the home team down by a run or more, the first batter steps up in the bottom of the inning.

The pitch to the leadoff batter looks just a bit outside and the ump calls, “Strike one!” You or a fan around you might yell, “C’mon ump! That wasn’t a strike three innings ago!” or, “Are you late for your dinner reservation, blue?!”

You’re not sure if it’s true, but in extra innings, it often seems like the home plate umpire makes ball-strike calls that will end the game sooner rather than later. If the home team is losing in the bottom of the inning, it might appear that the umpire’s strike zone has expanded a little bit, which favors the pitcher.

On the other hand, should the game be tied and the home team gets a runner on base, perhaps the umpire’s strike zone narrows, giving the home team batter an advantage that could result in the game ending sooner.

Of course, a fan’s perception of reality when it comes to umpires might be skewed. We have our rooting interests. We want our team to win. This desire to win only increases in MLB extra innings, when every ball-strike call is magnified by the intensity of the situation. Surely it’s our imagination that umpires are making calls to get an extra inning game over quickly rather than have it drag on?

It turns out it’s not our imagination. According to this article from Fivethirtyeight.com, umpires do have different strike zones in extra innings. Using a sample of around 32,000 pitches in the nine years from 2008 to 2016, they found that umpires in extra innings are more likely to make ball-strike calls that will end the game sooner rather than later.

House That Hank Built

Simply put, when the home team is positioned to win a game by having a runner on base in a tie game in the bottom of any extra inning, umpires in this study were more likely to call borderline pitches a ball.

This gives the advantage to the batter and would result in the game ending sooner. If the home team was down by a run or more in the bottom of an extra inning, those borderline pitches were more likely to be called strikes, giving the advantage to the pitcher. In both cases, ball-strike calls were made that would end the game more quickly.

The article at FiveThirtyEight isn’t the first time umpire calls on balls and strikes have been studied.

The book Scorecasting: The Hidden Influences Behind How Sports Are Played, and Games Are Won, had a section about how umpire bias accounts for most of a team’s home field advantage.

When that book came out, Dave Studeman had an article at The Hardball Times that summarized a John Walsh study that used two years worth of PITCHf/x data (2008-2009) to determine if umpires have a home team bias on ball-strike calls. It turns out, they did.

In the study by Walsh, it was determined that umpires have a slight bias towards the home team on balls and strikes. That bias makes up about one-third of the overall home field advantage.

It’s unlikely that umpires are doing this intentionally. In the case of extra innings, umpires are likely trying to make the calls with as much integrity and impartiality as they always do, yet human fallibility slips in. The same is likely true for ball-strike calls that contribute to the home field advantage in MLB.

Next: Fun fact rankings of American League ballparks

Humans are affected by outside stimuli. It could be hunger pains in their stomachs during an extra-inning game. It could be the home crowd having an effect that helps the home team get that borderline call. Whatever the case, human umpires have these tendencies, and it would be difficult to eliminate them. Robot umps, on the other hand…