The same way we do auto accidents? Collect what physical evidence is possible, interview witnesses, and attempt to assign fault.

And I'm not advocating for a return to duels at dawn with pistols!

But simple or criminal battery (e.g. I punch someone, with my fists, and then de-escalate) that could not have been expected to result in permanent injury? I can think of worse things for culture.

Auto incidents happen in relatively constrained scenarios, and the resulting damage can strongly imply the actions that led up to the incident. Not so with humans beefing over mundane matters.

My first thought is to re-tool the concept of self-defense, but this would require the acknowledgement that verbal abuse constitutes violence, which I am not sure many are willing to accept, and could get out of hand when it comes to what exactly "disproportionate retaliation" means in context.