Referees are supposed to be impartial. In academics, this is most of the time helped by the fact that they are anonymous. In sports, referees are public and meeting participants, including spectators, try to influence them. This becomes particularly relevant when the referee has to take a decision against the home team than leaves spectators irate. They could retaliate against him. Does this influence referees?
Andrés Picazo-Tadeo, Francisco Gónzalez-Gómez and Jorge Guardiola Wanden-Berghe look at first division football in Spain, carefully taking into account stadium capacity, how full it is, how far spectators are from the pitch, and referee experience. They find that awarding a free kick does not have a home bias, which is consistent with the fact that this is a split-second decision. The ensuing decision to give the offending player a caution is, however, affected by home bias. This decision is not instantaneous, and social pressure can be exerted on the referee, especially when the stadium is full. The presence of a running track that separates the local supporters form the action does not seem to matter, though. I wonder whether some teams have a larger home bias than others, as the fans' reputation could also influence referees.