Just so everybody knows this, the credit for this answer goes to @TaskMasters since he answered this same question on another post....
Spectator aggression happens due to intense feelings that fans feel when watching an event. This is particularly true when the venues are not adequate to hold a huge number of spectators, unruly fans who aggravate others during the event and the presence of alcohol that can stimulate aggression in fans. This is especially true when the athlete or team they are rooting for is losing the competition.
