In poker, reading the facial expressions  of others can be vital to sussing out a bluff. A similar situation may play out in baseball games, according to a new study in Frontiers in Psychology

In baseball, the pitcher and the hitter are essentially engaged in a duel, making the sport a great way to examine how interpersonal dynamics affect the game. In this study, Amsterdam-based psychologists tested how student participants reacted to footage of Major League Baseball players pitching in the World Series to see if facial expressions influence how people analyze the throws. 

After establishing in pre-tests that students could glean specific emotions from the videos, a group of 34 participants watched the clips of World Series pitchers just before they threw the ball and predicted how accurate the pitch would be. They ranked the likelihood of whether the pitch would be fast or slow, difficult or easy, and whether the batter would swing or not. 

The students predicted that pitchers with angry expressions would throw faster, more difficult pitches, while happy pitchers would throw more accurately. Unsurprisingly, worried-looking pitchers were perceived as not accurate in their throws. 

The Dutch students had very little experience with baseball, so the experiment probably doesn’t exactly match up to how a real game would unfold. However, the researchers did compare their lab data with the real-life outcomes of the pitches shown in the video, including how fast the pitch was, whether the batter swung, and whether they got a hit. In reality, the pitcher’s emotional expression was unrelated to the speed of his throws or how accurate they were (if it was a "ball”), but facial expressions did affect whether or not the batter swung. When the pitchers looked happy, the batters were more likely to take a swing at the ball. 

The results were only marginally significant, so this is far from a hard-and-fast rule. But it does suggest that emotional analysis and facial expressions do play at least a minor role in baseball. And that pitchers should smile if they know they’re going to throw a bad pitch.