Caveat: the bones in the hand are really thin.
It took me a few seconds to recover, but when I did it was to check his hand was okay, as we weren't wearing gloves.
He was fine. I had a headache for two days.
> [The werewolf] gave him a ringing slap and that would have ended it, except that it also pulled itself a little further up the tree and brought itself within the range of the Vimes Elbow.
> It justified the capital letter. It had triumphed in a number of street fights. Vimes had learned early on in his career that the graveyards were full of people who'd read the Marquis of Fantailler. The whole idea of fighting was to stop the other bloke hitting you as soon as possible. It wasn't to earn marks. Vimes had often fought in circumstances where being able to use the hands freely was a luxury, but it was amazing how a well-placed elbow could make a point, possibly assisted by a knee.
-- The Fifth Elephant by Terry Pratchett
A footnote from an earlier reference explains that:
> * The Marquis of Fantailler got into many fights in his youth, most of them as a result of being known as the Marquis of Fantailler, and wrote a set of rules for what he termed ‘the noble art of fisticuffs’, which mostly consisted of a list of places where people weren’t allowed to hit him. Many people were impressed with his work and later stood with noble chest out-thrust and fists balled in a spirit of manly aggression against people who hadn’t read the Marquis’s book but did know how to knock people senseless with a chair.
Using padded gloves allows for hitting the opponent much harder without injury to the hand, so they make it possible to hit with a lot more force. Serious brain injury is caused by accelerational forces, and those are only slightly reduced by the padding, but the padding gives significant protection to the thin bones of the hand. Without the protection the bones in the hand could break when struck against the relatively hardy bones of the skull.
Of course if you did happen to nicely hit the jaw, that's one of the common target spots for a knockout. A hit on the jaw causes a rotational force on the head which can more easily lead to a knockout (as well as injury to the brain).
In the Ancient Greece and then in the Roman Republic and Empire, there were 3 combat sports: wrestling, pugilism (i.e. boxing) and pancratium (i.e. MMA).
Punching was allowed in both pugilism and pancratium, but only the pugilists bandaged their hands with leather straps, to protect them from injuries (analogous to the big boxing gloves and the small MMA gloves of today).
Because of their bandaged hands, the pugilists were using hard strikes to the head much more frequently than the pancratium fighters, so finishing a fight with severe injuries was much more common for pugilists.
Some ancient writers have commented about this and they have mentioned that at big competitions like the Olympic Games it has been decided to schedule the pancratium matches before the pugilism matches, because there were some people who desired to compete in both tournaments. Had pugilism been scheduled the first, there would have been a high risk for them to be injured, preventing them to also compete in pancratium, while with pancratium before, they had good chances to be able to compete in both.
At the same time in Okinawa they preferred to use the fists, but that was right for them only because those using fists practiced daily conditionining of the fists by hitting a maki-wara.
Also today, for anyone who does not punch regularly some training device, hitting either with the open hand (edge or base) or only with the external side of the fist (hammer fist) is the right choice for any purpose.