Home field intimidation

According to a paper from Marshall Jones of Penn State in Psychology of Sport and Exercise (you can read it for only $31.50), home field advantage is far more prevalent in subjectively judged, independent sports, like diving and gymnastics, than in objectively judged sports, like sprinting and the biathlon.

Subjectively evaluated sports such as diving, gymnastics, or figure skating usually show sizable and significant home advantages. Otherwise, occasional findings have been reported but they are not consistent within a sport, are generally weak, and often statistically unreliable. – Marshall Jones

This dovetails nicely with the home field advantage phenomena reported by L Jon Wertheim and Tobias Moskowitz in Scorecasting for team sports like baseball, basketball, and association football (aka, soccer) on points of subjective judgments (eg, strike zone, certain fouls, and extra time, respectively).

Taking together, this suggests that home field advantage is a result of the crowd intimidating the officials, not the crowd boosting the morale of the home team.