Hotter Temperatures Mean More Hit Batsmen in Baseball

During spring training, Major League pitchers work on fine-tuning their mechanics and strengthening their legs so they don't break down during the dog days of summer.

It's doubtful these pitchers will give much thought to what the July heat might do to their brains, but perhaps they should.

A new study led by researchers from Duke University's Fuqua School of Business has found pitchers whose teammates get hit by a pitch are more likely to retaliate and plunk an opposing batter when the temperature reaches 90 degrees than when it is cooler. But if no one has been hit in the game, then high temperatures have little effect on a pitcher's behavior.

"We found that heat does not lead to more aggression in general," said Richard Larrick, a management professor at Fuqua. "Instead, heat affects a specific form of aggression. It increases retribution."

Major League statistics show there were 1,549 incidents of hit batsmen last season, an average of .64 hit-by-pitch incidents per game. Most pitchers are not intentionally beaning batters, as a hit batsman automatically proceeds to first base and increases the chances that his team will score, Larrick said. Despite that advantage, pitchers and team managers admit they sometimes target batters on purpose.

"When a batter is hit by the opposing team, his teammates don't know if it was an accident or deliberate," said Larrick, who also holds an appointment in the department of psychology and neuroscience. "We think hotter temperatures make a pitcher more likely to see the action as deliberate and hostile. And once a pitcher feels provoked, hotter temperatures increase feelings of revenge."

The study, which appears in the March 2011 issue of the journal Psychological Science, examined 57,293 Major League Baseball games from 1952 through 2009 -- roughly 4.5 million matchups between a pitcher and a hitter. Temperature was more predictive of struck batsmen if the opposing team's pitcher had already beaned one or more hitters. For example, if temperatures were in the 50s during a game, there was a 22 percent chance a pitcher would hit a batter if a precipitating pitch occurred in the first inning of a game. When temperatures were in the 90s, the retaliation risk rose to 27 percent.

To make sure other factors weren't confounding the link between temperature and hit batsmen, the researchers analyzed variables that might affect a pitcher's performance, including indicators of pitcher inaccuracy such as wild pitches, and other measures such as errors by the team, the year the game was played, where the game was played, inning and score.

"It was important to sort out whether heat tends to increase aggressive behavior, such as retribution, or whether it leads pitchers to be less accurate with their pitches," said Larrick.

Larrick, a longtime St. Louis Cardinals fan, first examined the link between heat and pitcher retaliation as a graduate student, but couldn't amass enough data -- at least not by poring through microfilms. He decided to revisit the question more recently because historical play-by-play game transcripts have been posted online by dedicated baseball fans.

As an expert in behavioral science, Larrick expected to find a connection between heat and aggression. "There are decades of research showing heat leads to aggression, like finding more violent crime in the summer," he said. "But in crime statistics, it's hard to really determine if it's heat or other things. One of the nice things about studying baseball is that we're able to control for factors besides heat."

Larrick said he was surprised that the "a batter for a batter" tradition of retaliation does not always hold. "Baseball fans will tell you the sport's code of honor dictates you're supposed to hit a player on the other team when your player has been hit," he said. "Nobody seems to be aware that players apply the rule much more at high temperatures than at cool temperatures."

Other authors of the study include Andrew Carton of Fuqua; Thomas A. Timmerman, Tennessee Technological University; and Jason Abrevaya, University of Texas.
The research report is available online at: http://pss.sagepub.com/content/early/2011/02/23/0956797611399292.full.pdf+htm

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