Does Bill James's Pythagorean Formula Apply to Football?

Abstract

In 1980, baseball writer and statistician Bill James developed a formula that related a baseball team’s win-loss percentage to the number of runs they scored and allowed.  This formula was modified in the mid-1990s for use in professional basketball, with points scored and allowed in lieu of baseball’s runs scored and allowed.   This paper empirically tests the modified formula using data on points for and points allowed for all 32 teams in the National Football League (NFL), by conference, from 2002 through 2020 (and during the two shorter periods, 2002-10 and 2011-20).  The authors find that the Bill James method works remarkably well for the NFL.  The authors’ regressions are also used to identify “overachievers” and “underachievers” during this period.