Where I grew up, a domestic dispute involved a cop coming out, telling people to calm down, writing down everyone's story and offering a card to contact someone about restraining orders.

In domestic cases, the line about "who started it." is often blurred to all hell, and when 2 people choose to attack each other, that's not a crime. If it's not clear that one person was an unwilling victim of assault, then what's the cop to do?

It's your choice to have a home MMA match.
So long as both people are free to leave, and neither leaves, then there's no victim and no crime, IMO.