DevinHammer

A few points to ponder:
If the fight is just getting started, or is still fairly even, one of the best things I've ever seen is to redirect or confuse their focus with something totally out of context. Walk up to them like nothing's happening and ask for the time, ask for directions, tell them there was an accident and you desperately need their help. That will often stop them cold. Then, you can ask them what they were fighting about. When they stop to think about it, they'll either realize it was stupid or possibly look to you as an arbitrator and you may be able to help them settle their differences.

If one of them clearly has the advantage and is just pummeling the other, the clear choice is to defend the underdog. You should be able to slip in next to the victim and use much the same blends and techniques as if you were being attacked. Alternatively, the safer method may be to slip in next to or behind the attacker as if you had already blended with his attack and execute a technique (like kotegaeshi) from there.