We exploit a natural experiment within each National Football League game, finding the first evidence in professional sports that referees succumb to the pressures of satisfying team personnel in the vicinity of possible violations. Using generalized additive models for binomial outcomes, we show that these sideline-based differences in penalty rates, which are observed on common but influential penalties including pass interference and holding, peak near the centralized location of players and coaches on the sideline. With sizable interests in referee decisions, coaches and players often try to manipulate referee behavior with verbal and nonverbal communications; such actions appear to be persuasive. (JEL ZO, H3)