Im of the opinion that bouncing is an “at your own risk” activity in regards to criminal/civil liability. A bouncer has no more “right” to lay hands on someone than any other person. And unlike police officers, they have no “qualified immunity” regarding their actions while working.
This guy has an interesting site regarding bouncers and their training.
State by state mileage may vary, but unless you are defending yourself or effecting an arrest, you risk arrest using force on someone. Some states allow bouncers to enforce trespass charges within the bar/club, but that can be a fine line. If a person is being rowdy in a movie theater, the ushers dont rush in and beat the crap out of the guy and toss him to the curb.
This being said, MOST of the bouncers I have dealt with (professionally), use common sense and typically just usher a loudmouth out w/o having to lay hands on him. If it looks like a fight they call us. If he starts a fight than they do what they have to do and then call us to have him arrested.