When the head is moved violently, the brain moves around in the skull. The heaviest part of the brain puts a lot of pressure on the brainstem, which can be twisted and pulled during the blow as the rest of the brain moves out of place.

What causes a knockout?

Retrospective analysis of boxing knockouts has revealed that they typically are caused by a hook to the side of the jaw which causes a rotation of the head in the horizontal plane. Uppercuts to the chin may also cause unconsciousness, while straight punches to the face are unlikely to do so (6).

What does being knocked out feel like?

While you're out, it is akin to being asleep. I have awoken as if from a deep sleep, and actually have felt extremely refreshed, that is, until the numbing pain of the strike that caused the forced nap flares up.