If you get punched in the nose, your eyes will water a lot, even if it didn’t really hurt
Your body follows your head. Your head gets pushed one way, your body will want to go that way.
Getting hit in the stomach isn’t good, it hurts. Getting hit in the diaphragm (between stomach and chest) is worse. Causes your lungs to kind of spasm and make it hard to breathe.
When fighting a larger person, they will have an easier time forcing you back.
The jaw is the knockout button. Hit it hard enough, and you’re down for the count.
Back of the head is very vulnerable. Can cause serious damage if hit there.
Kidney punches hurt a lot
People with experience will try to be where they are comfortable. A wrestler will fry to get their opponent on the ground, a boxer will stay on their feet, etc.
Easier counter to a kick is to get closer to whoever is trying it, then they won’t have enough room for it to be effective.
If you want realism, avoid fancy, flashy moves. They’re less practical and easier to counter.