I know this may sound stupid but, how do you write what happens after the punch hits to person? Like, when the punch hit “Their head flung/snapped sideways” Is there a word/words to describe that moment?
This isn’t a stupid question. After all, if you’ve never punched anything before or spent a lot of time around martial artists or practiced martial arts then you’re not going to be familiar with the after effects.
You can use many different words to describe a punch hitting someone, so there aren’t specific words you need to use. Some descriptions are better than others. You generally want to follow the rules of physics and force projection. The head is a decent example for big motion, outside the rest of the body, because the only structural support is the neck. When struck with a single hand instead of in dual motion (like say boxing the ears), the head will generally move in the same direction the force was applied.
Forward = back
Struck from right = swings toward left side (follow the force)
Struck from left = swings toward right side (follow the force)
Behind = forward
Under = Up
If you hit them hard enough they might be knocked off their central axis, at which point they will step in the appropriate direction to counter the incoming force. If enough force is applied to knock them off balance, they may stumble. Keep in mind stumbling is unlikely on the punch, especially against someone who knows how to set their balance, because upper body strikes aren’t as powerful as they’re presented on television.
So, if you strike someone in the face with a jab then their head might “snap backwards” or be “knocked backwards” depending on how hard they’re hit. The question is the image you want to present, verb “snap” implies a quick jerk where the reader might assume “knocked” affected more than just the head and led to a step backwards to regain balance. So, you might apply “snap” to a quick strike off the leading hand and “knocked” to strikes off the secondary power hand. I won’t say “left” or “right” because the hand positioning relies on which side of the brain is dominant. If you’re right handed then the right is most likely your dominant hand and your power hand, while the left is the front/light/fast hand. Vice versa for the lefthanded side.
This is just the head. If you were to punch someone in the stomach, their whole body would curl inwards to protect the injury and because all their air got knocked from their lungs. They might step backwards, they might fall to their knees.
Like with all writing, you want to think in depth about the verbs you’re choosing for your action sequences. Action verbs are not interchangeable. The question of “what is the physical response to someone being punched?” is reliant on the type of punch and where the punch lands. In a broad sense, you need to consider the point of impact and how far that impact is off center. You can consider center as the center line running up the middle of your body, strikes to that center, particularly in the upper body, are more likely to knock an opponent off balance. Not every punch will destabilize an opponent, not every punch will move them in an obvious way. Strikes to the shoulder, to the arm, to the legs, will cause responses in those single targets. The lack of an immediate, obvious reaction in those areas doesn’t mean the strikes are worthless. Punching someone in the shoulder can make it more difficult for them to lift their arm, which hinders both attack and defense.
Samantha knocked Joe’s arm away. With her right hand, she punched him in the shoulder. She didn’t wait for him to flinch, backhanding him across the temple. Joe’s head snapped sideways, and he stumbled. Seizing Joe’s loose wrist, Samantha drove a roundhouse into his stomach.
“Knocked” gives the impression of something going flying. Samantha “punches” him in the shoulder, which is a straightforward straight punch. Then, because she’s close, she “backhands” him with the same hand. Due to the force coming sideways, his head moves in the direction of the force inflicted, and, because it’s off center and he wasn’t expecting it, he stumbles. Then, Samantha grabs the arm he left free and kicks him. This is an age old tactic that works better with a sidekick, but the general idea is that you hold onto your opponent while delivering a powerful blow so the force cannot be mitigated by them moving backwards. They have to stand there and take it.
In hand to hand combat, some measure of force delivered will be mitigated by movement and some will be absorbed by you on the moment of impact. This is why you lock your joints and muscles in the moment before the strike, and why you can injure yourself when hitting someone else. While these are technical details which will slow down your scene with experienced combatants, they become an important point with inexperienced ones. Inexperienced fighters will tense up too early or too late on strikes, resulting in them being slower and failing to put all the force they’ve generated by their momentum into their opponent. They will also stop their strike before or at their opponent’s body instead of striking through them. This limits their force projection and, again, halves what they put into an opponent. In context, this is what martial artists mean when they say beginners don’t hit very hard.
What you need to do is practice visualizing the scene you want, then finding the words to describe it. When writing fight sequences, familiarize yourself with much imagery regarding the subject as you can. I recommend searching YouTube for How To videos on various martial arts and paying close attention to what happens when these various martial artists strike pads. Even when you’re not looking at someone fighting another human being, seeing how the impact affects the pads can be instructive for describing different situations.
The answer to finding the right words is trying out different verbs and different descriptions until you find ones that evoke the imagery or feeling you want for your scene. Unfortunately, this latter half is part of being a writer. There’s no right way to do it. The authenticity of the sequence will come from how well you portray your physics on the page. Almost nothing you write will come out perfect off the cuff. Ultimately, in this case, practice makes perfect.