Sub-Perfect Game: Profitable Biases of NBA Referees∗

This paper empirically investigates three hypotheses of biased officiating by National Basketball Association (NBA) referees. Using a sample of 28,388 quarter-level observations from six seasons, we find that NBA referees make calls that favor home teams, teams losing during games, and teams losing in playoff series. All of these biases are likely to be profitable to the league. We identify these effects as caused by referee bias, as opposed to player behavior, by using play-byplay data that allows us to separately analyze turnovers over which referees have relatively high or low discretion to judge. We also find that the biases do not increase in situations where their direct financial benefit to the league would be greater, and conclude that the biases are likely of