It may be better

to act to defuse the overall level of violence rather than to take sides - try to talk the combatants down, showing disapproval towards violence from either side, but indicating approval of rational action and discussion. Block and restrain the aggressors rather than flattening them. This probably takes more than one person.
If you are outnumbered or outgunned, common sense indicates a withdrawal. If a brawl is in progress, even the most proficient martial artist would be better getting out of there, and calling for reinforcements, the police usually being the best bet.
The martial artist is not a superhero and, usually, not an officer of the law. You and others have a right to defence, but not to punish others. Guilt and punishment are matters for the law.