Please provide the statute that says a cop, or anyone else, can grab you as you are leaving a building you were told to leave. Cops have no more right to grab you than anyone else.
The student was doing what he was told to do. Grabbing him at that point was battery.
Oh really? Was he told to incite others to join his "resistance".
Was he told to repeatedly refuse to produce his ID?
Bullsnot.
Show me where a police officer does not have the right to grab your arm and escort you from a premesis upon which you are trespassing?
California Penal Code section 242: "A battery is any willful and unlawful use of force or violence upon the person of another."
Now tell me, are you a first year law student or just a naive anarchist?