BtBS: A Magic Number to Increase Your Odds of Winning

Joe Lemire from Sports Illustrated wrote a piece a while back detailing this very thing. He calls it baseball’s magic number but I like to look at it as the Rule of 39. [...]

Peterson asked the team’s analytics department to research the correlation of winning percentage with the number of batters faced in a game. That research, he said, found a tipping point between 38 and 39 batters faced.

—snip—

Here’s why: Since 1991 home teams that have faced fewer than 39 opposing batters in a nine-inning game—four full times through the lineup, plus three additional hitters—win roughly three-quarters of the time (74 percent) while teams that have faced 39 or more hitters have won only 31 percent of games.Moreover, in the last 22 seasons home teams that have faced 39 opposing hitters have won almost exactly 50 percent of their games—50.082 percent, to be more precise—making 39 the inflection point of winning or losing.