Fan on the court? Fan leaves. Game doesn't start until fan leaves. If fan doesn't leave and team identity is clear: forfeit.
I had a Dad in the top row during a CYO tournament championship get very abusive at my partner. I just walked to the bottom of the stands and pointed to the door. He refused. I walked to the table and in a loud voice said, "Put :30 seconds on the clock and if he is still here when the horn sounds the game is over!" and then walked away. The other parents almost bodily threw him out since their team was winning at the time.
