Field of Science


Baseball Players Make Worse and Worse Decisions as the Season Goes On

If their goal were to frustrate fans, they couldn't plan it any better. Major-league baseball players reach a low point in their decision making in September, just in time for playoffs. Across all teams, batters swing at more and more pitches they shouldn't as the season goes on.

They may just need a nap.

"Consistently getting too little sleep—even if it's just [by] one hour a night—can lead to a state of chronic sleep deprivation that can compromise performance," says Vanderbilt University neurologist Scott Kutscher. "Specifically, things like judgment and reaction time."

Judgment and reaction time are just what a baseball player needs when a ball is hurtling toward his body at 90 miles an hour: he has to decide whether to swing, then react quickly enough to actually get it done. And sleep deprivation is familiar to pro ball players, who have a packed schedule and frequently travel back and forth across the country.

To see whether baseball players suffer the effects of sleep loss as the season drags on (or skips along for six non-tedious months, depending on your inclinations), Kutscher and his colleagues looked at data from 2011 back to 2006, after the MLB cracked down on steroid use. For each team, they tracked how often players swung at pitches outside the strike zone.

Over the course of the season, the researchers saw a steady increase in how many out-of-the-strike-zone pitches players swung at. These badly judged swings went up by about six-tenths of a percent each month.

Then Kutscher and his colleagues tested that model on the data from the 2012 season. When the numbers from all the MLB teams were pooled together, the model was a tight fit. Out of 30 teams, 24 were swinging at more balls in September than in April. Kutscher presented the findings at a recent conference on sleep.

Other factors aside from sleepiness may be at work. Pitchers might be throwing better curveballs as the months pass, for example. But Kutscher says pitchers threw pretty much the same ratio of balls and strikes throughout the season; if they were improving a lot, you'd expect to see them throwing more strikes. (Not to mention that batters, too, are practicing and honing their skills during the season.)

Since the researchers looked at whole teams rather than individuals, it's also possible that a change in the roster during the season—say, the addition of less experienced players who are called up from the minors—has an effect. Kutscher doesn't think this could account for all the deterioration he witnessed, though.

"I am hesitant to argue that fatigue is 100% of the story," Kutscher says. "But we have findings that are consistent with what we know about fatigue and chronic sleep loss."

Pro ball players, and other athletes, might see their performance improve if they could avoid sleep deprivation. So stop shouting at that guy on your screen who just struck out—he needs to go home and get some rest.

Image: Ed Gaillard (via Flickr)

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