This paper builds an economic model of referee behavior in the National Hockey League using period-specific, in-game data. Recognizing that referees are influenced by a desire for perceived fairness, this model isolates situations where a referee is more likely to call a penalty on one team. While prior research has focused on a systematic bias in favor of the home team, we find that referee bias also depends upon game-specific conditions that incentivize an evening of penalty calls. Refereeing games in this fashion maintains the integrity of the game, thus benefiting spectator perceptions and opportunities for financial returns.