Wow, surprised to hear IT did this. I agree with some that fans don't have the right to say whatever they want just because they buy a ticket.
When I go to a game, I root for my team, eat my food, drink my drinks, cheer and go home. However, a fan saying "F-U" to a player shouldn't elicit a response from IT to jump into the stands.
Shame on the fan because there's kids around and it's common courtesy not to swear in public. If the fan said something personal about IT, then I can see it.
But just for dropping the f-bomb, I don't think it was necessary to do what IT did. At the very least, just give him the finger back.