It's as per Canadian Criminal Code and Law... and it's entirely upon how you articulate it all on the stand, and for each person it's different. For example. A tiny 4' female fighting a 6' MMA-looking male very well might be able to articulate that she felt her life was in danger with him just about to punch her, so she shot him dead. Doubt a 6' MMA-looking male against a 6' MMA-looking male could articulate the same and have it believable.
I can't fathom how one could argue they felt their life was in danger from the act of the rider punching at the window. I'd suggest 100% of the time that act alone won't result in you dying.
Aaaaaaaaaaaaaaaaaaaand, you didn't answer the question.
Anyways, all the driver needs at this point is plausible denial. A former attorney general managed. As did that guy who DID get the snot beat out of him.
Starting stuff on a bike with a car or truck, is like bringing a knife to a gun fight, and trying to start something!