Many fights start out benign but evolve into something more dangerous. For example someone responds to a shove with a punch to the gut, and he responds with a punch to the fight, and it escalates.
Say Joe and Bob are get in an argument and Joe shoves Bob. Bob punches Joe and Joe hits him back. Can Bob sue Joe because Joe technically touched Bob first by pushing him?
I know self defense is only valid if reasonable force is used, but how exactly does this work? For example if Bob hit Joe and Joe hit him back and knocked him out, just because Joe won the fight doesn't mean that he loses in court?