Here’s renowned self-defense instructor Kelly McCann talking about rage and it’s place in a fight. He also talks a little bit about legality and why jumping in fists swinging just isn’t a good idea.
When working with this in a writing context, it’s important to remember when you’re building characters to moderate their aggression. Combat is about control, controlling your opponent and keeping control of yourself. It’s important not to confuse guided rage with berserker, and also important not to confuse those things with “professional combatant”. No matter who they are, your characters are going to be working within the boundaries of some sort of legal system.
So, try not to go hog wild.