It is in your driveway...it concerns you. If dude was her father...who the hell is the guy assaulting the girl? You can't spank your little kids...and you can't slam your teen against the car...it is child abuse.
At this point I would follow medicine man's advice...rack a round...tell 'em to stop...
Although you had only a bike flashlight...you are clearly a super hero...hypnotize them with your magical green thumb.
In light of current events, better a girl is let go, and if in fact is a minor run-away, then a third party who is not tied up emotionally could resolve the issue (without the bruises). The girl is screaming for help...could you live with yourself if she was abducted and killed...and you did not kick the guys ass...or throw your flashlight at him???
In all sincerity I would 1. not have gone out unarmed (but I am not a super hero!)...and 2. this
may actually be a case when one should call the cops...though that is a hard one to swallow.