Fighting should always be last resort for a bouncer... I used to buy people drinks, and try to talk 'em into shaking hands... Fun part is that it worked most of the time. The rest of the time, it was several guys escorting the miscreants to the door - separately.
One time had a coupla guys getting frisky, and I figured that the "shake hands" method wasn't gonna work - they looked like "let's fight for fun" folks... So out came a can of pepper spray for an off-the trigger wave-around... "You guys don't wanna do this, so let's play nice-nice..." And since they didn't want any bear seasoning, they did...
BTW, any time they had folks getting frisky, one of the bartenders was glued to the cash registers, with his hands a short move from a 12 gauge...
Most violent thing I ever saw tho was a guy, probably a vagrant, who tried to hold up a bar with a butcher knife. On darts league night. Sucked to be him.