I know we’ve said this before, but hand to hand combat takes a toll. Even if you get through a fight “unscathed,” you’re still going to have bruises on your arms from parrying, skinned knuckles, and your body will ache the next day. That’s if you know what you’re doing, and keep full control.
Any attack that lands, or misjudged strike that connects with a wall will hurt, and those can turn into serious injuries quickly. If you don’t take time to recover after each fight, the strain builds up, quickly.
An imperfectly tensed punch can easily break bones in the hand. This is something that actually happens to boxers, people who, as you might expect, have a pretty solid grasp of how to drive a fist into their opponent.
Also for a lot of untrained combatants, preconceptions on how violence should occur, will actually work against them. The example that comes to mind is simply trying to punch your opponent in the face. While this might have seemed like a good idea at the time, it’s after the fact that you realize your face is a mass of bones that are very close to the surface, and while the punch will hurt them, it will also hurt you far more than if you’d simply driven a fist into their gut and called it a day.
The other side of this is, if nothing’s broken, you’re not bleeding internally, and you didn’t tear anything, the hospital isn’t actually necessary. Cuts, scrapes and bruises heal. Muscle aches eventually fade. The entire experience may be singularly unpleasant, but it’s entirely possible your character could walk it off afterwards.
The hard thing with this kind of violence is making sure your character puts enough time between their fights, so their body can fully recover. That will take months, and there’s nothing a hospital could do to accelerate the recovery time.
But, this the first time they break something or tear a ligament, then this will have caught up with them. That could easily be their first fight.
Perhaps ironically, given its reputation, Fight Club by Chuck Palahniuk is an excellent gross out fest if you want to think about what happens when untrained combatants go at each other full tilt.
I always liked the part where the narrator is giving a presentation to his bosses while bleeding profusely from his gums due to a fight from the previous day.