This article examines the impact of on-the-field rule changes on competitive balance in the NFL. This is done using the Herfindahl-Hirschman Index and other team statistics from 1970 through the 2016 regular season of the National Football League. Using a Two-Stage-Least-Squares regression this study’s results do not support that on-the-field rule changes may impact competitive balance. This study's findings are companionless with respect to related literature.