I have neither the time nor the writing ability to be able to adequately answer what is an interesting question but I want to give it a go.
For me fighting is not simply about testing yourself against someone else or hurting someone you don't like although those can definitely be elements about it. It's about that rare time when you can, for once, let everything out, where you can break free of all (or at least most) rules. That freedom is exhilarating and once you're in that place with someone else and that you have both given it everything that is when a victory really feels like a triumph and a defeat truly hurts and humbles.
After a fight a winner can pile more misery on the loser with some stakes or something that wasn't planned but for me the biggest humiliation is that someone else saw me 'go to that place' but still came out on top, that's the sort of thing which stays in your head long after physical wounds have disappeared.
