You can trespass someone from an organization (and thereforeits functions), not just a specific venue.
At least that's how a DA splained it to me once. She said it isn't gray, but restraining order should follow to give it teeth.
No idea if true or if state to state.
Let's say I put on dances in different venues and someone has become a problem at each one.
As long as I am charging a fee and am responsible for security, I have the right to say who comes in. You have no right to be there even if you purchased a ticket.