Because he isn't in front of the car, he's just at the side. He hasn't told that guy to stop. Therefore that guy has no legal obligation to stay where he is. He starts the engine and does nothing, moves slightly and still does nothing, and only at the last minute acts like a faggot drama queen.
This guy has every right to sue the fuck out of that guy, he's not clearly told him to stop. He's standing at the side, only moving slightly when the engine starts. And then physically attacking the guy and verbally insulting him for running over his foot, he can walk pretty fucking well for a guy who's foot just been ran over.
Where I am you're legally allow to drive away if someone is writing you a parking ticket, it's only final if it actually gets put on your window.
Sucks to be a cop.
