The social facilitation principle contributes to such behavior as our performance is enhanced in the presence of others. Thus, a person in a crowd will probably yell or boo in a louder way than if he/she was by himself/herself. Also, the deindividuation principle refers to the change of behavior of a person influenced by a crowd. Thus, people in a crowd may lose self-awareness/inhibition and act in a more aggressive way (such as throwing cups/trash at the players after they lose the match.
