Lama Ole’s answer:
That depends on how many of them there are, how serious it is, and what one can do oneself. But in a brawl, under no circumstances should one judge who the good guys and bad guys are, even if a couple of brutes are running off with an old lady’s purse. Of course you should try to stop them and give the lady her purse back. But you cannot judge because the old lady certainly did something to them earlier. Everything is cause and effect.
What you can do is try to calm the situation down and bring in your abilities where you can. Look at the situation: Are a couple of drunks beating each other? Are they about the same size and strength, and does neither have a knife? Then you don’t necessarily need to throw yourself in between them.
But if one of them is clearly at a disadvantage and the other is a brutal sort, or if there are weapons involved—then call the police as quickly as possible. You pay taxes so that help comes in such cases. Whoever is strong enough can pull the people apart himself and push them up against the wall a few times until they calm down. If there is no anger involved, then people become like wax in your hands. You will be amazed. Even the most brutal guys will give in if you act without anger. They know that it is a higher power and they disappear. And you don’t only help the weaker person through intervening; the stronger one also won’t be happy if he flattens the weaker one.
By the way, as a woman one can always stand nearby and scream really loudly. That helps surprisingly well.