A good powerful kick or punch, thrown to the right place, can stop anybody. Except for the guys it can't. (and there's always some of those sons a bitches around)
Yes…and mostly …. it looks like it is those SOBs that somehow take us on. The ones who have had street fights before and enjoy them and know they can do damage, alone or with their buddies.
As Otto points out as well is that even people shot center mass at times will not stop in time before they kill you. So the fantasies of 'stopping' with empty hands 'killer blows' must be toned down.