PITCH COUNT AND PITCHER EFFECTIVENESS
In October 2003 the Red Sox were leading the Yankees 5–2 after seven innings of the seventh and deciding game of the American League Championship Series. Pitcher Pedro Martinez was cruising along and had allowed only two runs. At the start of the eighth inning Martinez got the first batter out, but then Derek Jeter hit a double. Red Sox manager Grady Little went to the mound and talked to Martinez, and then left him in the game. The Yankees promptly tied the game and went on to win in the eleventh inning on a dramatic walk- off home run by Aaron Boone. Grady Little was fired later that week. Most baseball analysts think that one reason Little was fired was that he ignored Martinez's tendency to become, after throwing 100 pitches, a much less effective pitcher. Going into the eighth inning, Martinez was well over the 100- pitch count. Batters facing Martinez after he had thrown fewer than 100 pitches had an OBP of 0.256.1 This meant that before Martinez had thrown 100 pitches, a batter had a 26% chance of reaching base. After Martinez had thrown more than 100 pitches, batters had a 0.364 OBP, or a 36% chance of reaching base. Since the average OBP is 34%, when Martinez has thrown a lot of pitches he becomes less effective. Grady Little ignored this record, and in all likelihood (since the Yankees had only a 10% chance of winning the game at the start of the eighth inning) his decision cost the Red Sox the 2003 American League championship.
Teams whose front offices' philosophy is data- driven keep records of changes to a pitcher's effectiveness as he throws more pitches. In The Book, TLD cleverly analyzed how a pitcher's effectiveness varies with the number of pitches thrown. Using every plate appearance for the 1999–2002 seasons, they analyzed how each hitter performed (after adjusting for the individual abilities of the hitter and pitcher) for every time a pitcher worked through the nine- man batting order.2 This measure of hitting performance
1 Adler, Baseball Hacks, 358.