Ding Ding Ding! People don't get thrown out of bars for nothing. Well, actually, they do. It is private property. If the bartender doesn't like your hair, that is a good enough, and lawful reason to have you removed from the premises.
But that wouldn't be justification enough to assault you.
Bartenders do have the right to physically remove you if you are asked to leave, and you show the slightest passive movement. If you don't get up and leave immediately, they will force you out. Sometimes when we are forced to move, our feet don't know what to do, and we stumble, especially if we are inebriated. Sometimes causing bumps, bruises, and the occasional bleeding.
With that said, I am a police officer, and do come across this situation. 97% of the time, it is the drunk that is causing trouble and doesn't want to leave, so he is forced out. The other 3% of the time, it is a person that thinks they are asked to leave for no good reason, when in fact, any reason is a lawful reason.
We hear this a lot in the field. "I didn't do anything."
If you think you were wronged, get an attorney. Get the name of the officer(s) that told you not to do anything about it. File a complaint with their supervisor(s).