Bare fists fit into a lot of places that gloves cant so its as much about the target zone as it is about the type of strike. The protruding knuckle can go into the exact temple region with penetration on a back fist or a hook and the ungloved hand or the mid finger knuckles,blade of the hand and outside of the wrist fit in under the jawline where the aorta and jugular cross in the neck.
If you dont know how to wake some up out of that kind of brain freeze its possible their heart can stop. You'd think it would of happened by accident at rare times in the old days without gloves besides the added percussive damage and brain bleeds over the longer rounds. Lucky they had shit house foot wear or it may have been worse for them.