Noah Davis and Michael Lopez did a statistical analysis of referee calls in American football:

• An study of NFL games found that referees call more penalties against the defensive team, when they’re standing on the offensive team’s sideline, and vice versa.
• The effect is most prominent when the referee is standing in the area of the sideline that substitute players and coaches normally sit.
• The effect is large – at times it can increase the amount of penalties called against a side by as much as 50%.
• Referees must make calls in real-time without replays. Evidence shows that they’re affected by crowd cheers and boos. It’s unsurprising that having an angry coach yell into their ear also affects decisions.

See some fascinating visualizations of the effect on FiveThirtyEight