Re: Techniques for breaking up a fight.
I think Nike-waza is a good technique.
Definitely don't do what I did over twenty years ago, and stick your mouth in the way of one of the fighters' friend's fists, and lose a tooth. Not a lot of fun to get emergency dental surgery in the hospital. On New Year's Eve even...
That, by the way, is what prompted me to start practicing martial arts. Haven't even been close to an altercation since then. Go figure.