BRJ: Hitting Streaks Don’t Obey Your Rules

On Saturday afternoon, Dodgers outfielder Andre Ethier’s 30-game hitting streak was ended by a trio of Mets pitchers: Dillon Gee, Mike O’Connor and Tim Byrdak. It was the longest hitting streak of the early 2011 Major League season, just over halfway to Joe DiMaggio’s vaunted record of 56, set in 1941. Ethier finished one game away from the Dodgers’ franchise record of 31 games, set by Willie Davis in 1969.

In 2008, SABR member Trent McCotter studied all games over a forty-year period (1957-2006) to determine whether a player’s performance in one game has any predictive power for how he will do in the next game. McCotter wrote:

If a baseball player usually has a 75 percent chance of getting at least one base hit in any given game and he’s gotten a hit in 10 straight games, does he still have a 75 percent chance of getting a hit in the 11th game? This is essentially asking, “Are batters’ games independent from one another?” …

Most statisticians will say that the batter in fact does still have a 75 percent chance of getting a hit in the next game, regardless of what he did in the last 10. In fact, this assumption has been the basis for several Baseball Research Journal articles in which the authors have attempted to calculate the probabilities of long hitting streaks, usually Joe DiMaggio’s major-league record 56-game streak in 1941. It was this assumption about independent that I wanted to test, especially in those rare cases where a player has a long hitting streak (20 consecutive games or more). These are the cases where the players are usually aware that they’ve got a long streak going.

According to McCotter’s research, “almost three times as many 30-plus-game hitting streaks have occurred in real life as we would have expected.” He examines several explanations for this finding: 1) Do players who have long streaks change their approach at the plate, going for fewer walks and more singles? 2) Are official scorers more generous to hitters so as not to “break” the streak with a borderline call — such as might have been the case with Ethier’s hot-shot grounder off a fielder’s glove on Sunday? 3) Do some hitters experience a “hot-hand effect,” where they become more likely to continue a long streak? 4) Does the weather have an effect on long hitting streaks, perhaps? 5) What about the quality of the opposing pitching?

Read “Hitting Streaks Don’t Obey Your Rules: Evidence That Hitting Streaks Aren’t Just By-Products of Random Variation” (BRJ 37, 2008)

Note: This story has been modified from its original version.

Originally published: May 2, 2011. Last Updated: May 2, 2011.