For three common penalties, the direction of the play — that is, whether it’s run toward the offensive or defensive team’s sideline — makes a significant difference. In other words, refs make more defensive pass interference calls on the offensive team’s sideline but more offensive holding calls on the defensive team’s sideline. What’s more, these differences aren’t uniform across the field — the effect only shows up on plays run, roughly, between the 32-yard lines, the same space where coaches and players are allowed to stand during play. ...
The most common cue in sports is crowd noise, and because crowd noise almost always supports the home team, the way the fans sway the referees is the No. 1 driver of home-field advantage in sports. And one notable experiment suggests that how loud a crowd is helps refs decide whether an interaction should be penalized. A pair of German researchers showed actual referees old video clips of possible soccer infractions, with crowd noise played at high or low volume. Refs looking at the exact same interactions were more likely to hand out a yellow card when they heard a lot of crowd noise than when the volume was low.
It follows, then, that screaming and hat-throwing football personnel may also have an effect on referee choices. In football, this sideline bias even seems to supersede refs’ tendency to support the home team: The differences in the penalty rates from sideline to sideline are several times larger than the differences in penalty rates between the home and away teams.
--Noah Davis and Michael Lopez, FiveThirtyEight, on the power of lobbying