When that punch lands - and it feels like time stands still for the length of a whole heartbeat - one of two things happens next. The recipient, their face frozen at the point of impact, will crumble to the ground on rubber legs; their body rattling across the canvas until a thundering follow-up blow spikes them into stillness. Or their face won’t freeze at all. It will only wince (or maybe even grin!) as the punch glances off their chin like a hammer sparking off of an anvil.
But why the difference? What is it that makes different fighters able to tolerate different amounts of force to the head without being staggered, knocked down, or knocked all the way out?