I'm asking this here since I guess it's more to do with physics
Is it easier to knockout someone with a blow to the chin if his lower face is shaped like pic A than pic B? I'm assuming the head will yank easier and cause the brain to slam inside the skull
Also would a bigger skull provide more punch resistance or just an easier target?
No, the structure has very little to do with it. It has more to do with how dense you can make your jaw when you receive the impact. Which is why mouthguards are a really good thing. But in the end it doesn't matter what you do, if you're getting hit by a force strong enough to knock you out you're going down no matter what.
I guess A is easier to knock out because the lever to the brain is longer. However, this isn't the only variable by far. If you have a huge jaw, then it's harder to knock out too, because it's heavier and the muscles around it are stronger.
A knockout punch is actually about applying torque to the brainstem, or shocking the trigeminal nerve root. Snapping their neck around as quickly as possible.
I've got me some good ol trigeminal neuralgia, so I can ell ya pretty gosh darn quick the face has the densest concentration of nerve endings in the body. The 5th cranial nerve is also novel in how it connects to the brain. Supposedly, this allows it to overload the brainstem if it receives a significant trauma, though in truth I think it's largely mechanical stress to the brainstem. It's well known a blow to the back of the head can easily knock someone unconscious, and there are two deep brain regions that when blocked via transcranial magnetic stimulation, induce immediate unconsciousness. Perhaps shock travels to these structures? I don't know.
Anyway, this question is a bit difficult to answer. You'd need to assess thresholds for force to induce a knockout to each jaw type, then compare this against an average person's strength and the angle required to maximize force delivered in a fight. You could also approach it mechanistically, but no one has really fully reverse engineered the human body.
Intuitively I'd say the square jaw is more susceptible to a knockout. Don't know.
I'd have to say pic A to make an easier knockout, because when you apply force in the upwards direction it only distributes in one area; since its closer shaped to a trinagle. Whereareas Pic B, if you punch him up in the same manner as A, the force would distribute evenly; due to having a rectungular like face also at jawline being a little longer.
I'd say a bigger skull in terms of rectungular shape oppose to the triangle one would provide a bigger resistance due to its force distribute and facial shape itself.