An altered state experienced by participants and/or fans of a sporting event which render them incapable or rational thought. It can occur before, during, and after the event. Face painting and conspiracy theories are all examples of people experiencing competition psychosis.
Dude 1: Can't believe how those refs were cheating my boys.
Dude 2: They lost by 40.
Dude 1: The refs hated us.
Dude 2: You got a bad case of competition psychosis if you believe the refs were the reason for that ass kicking.