We are responsible for the safety of the players. That is dangerous behavior. that is also ludicrious behavior at a 6th grade game. Evidence Exhibit 1,243 in the Ignats theory that grownups shouldn't be allowed to attend kids' games.
Personally, he's lucky all I did was embarass him. And yes, I would personally ask him to leave and point him out to the site administrator. The game doesn't start until he is gone.