Legal Question in Personal Injury in California

Re: Assault

When your girlfriend refused to leave she became a trespasser. Your former friend was then allowed to use reasonable force to eject her. Whether the force he actually used was reasonable will depend upon the circumstances. Without more details I can't say whether his actions were reasonable.

Note, though, that the force used against a trespasser normally would be used to force her out of the premises. Throwing her to the floor would not accomplish this goal. Depending upon what else happened, though, the events you describe might have been reasonable.