Depends upon many things - whether you're the prick who started it, whether you're getting a beating, who is around you/the environment how much adrenaline you have, how your previous experiences have taught you to respond, etc.
In my case, a childhood of abuse and bullying meant that when somebody attacked me, nothing they did could hurt me and I was furious, but completely calm on the surface, batting their fists away and avoiding their pissed up attempts at kicking. They were more scared by my doing that than the full on, rolling on the floor catfight shit they thought counted as fighting, so they immediately retreated, screaming abuse, turning to run away when I reached the point of 'I've had enough of this shit now' and took a step towards them. I only did that because I was cornered - had I seen an opportunity to get away, I would have taken it immediately, as being in a fight is never anything to prolong.
Other people would be terrified and cower down whilst trying to protect their head. And others would feel red mist descend.
It's not anything big or clever.