Run Support Index: Determining a Run Support for Pitchers since 1901 and Adjusting Their Won/Loss Records

Chris Jaffe

Presidential Ballroom III

This study consists of two main features. The first is a statistic Chris invented called Run Support Index (RSI). This is calculated by examining the game logs at Retrosheet and finding how many runs were scored in each pitcher’s starts; dividing by his total starts, the batter park factor listed at baseball-reference.com, the league average, and multiplying by 100. Like ERA+, it is centered on 100, and a pitcher with an RSI over 100 had above average run support. Chris rounded single season RSI off to the nearest integer, and for career RSI he calculated it to the hundredths decimal. Chris calculated the RSIs for over 150 different twentieth century pitchers including all whom are either: in the Hall of Fame, listed in the top 100 pitchers of the New Historical Abstract, or had more that 392 starts. Altogether, over 65,000 starts and over 2000 seasons where a pitcher started at least 25 games have been figured for RSI. To adjust for won/loss record, Chris used the Pythagorean formula to determine a pitcher’s expected won/loss record with both his actual run support and with league average run support. His real won/loss record is adjusted by the difference between those two factors.

Christopher Jaffe is a Ph.D. candidate in American history at Northern Illinois University. He resides in Schaumburg, Illinois and is a Cubs fan.