Dan, that's 21 ft only with a man carrying a knife. It doesn't take long for a dude under the influence to cover that ground and stick you with that knife. In the training world, some police academies and many private training facilities practice knife defense. In some training scenarios, a guy will come at you with a dummy knife and you try to get him with good hits using paintball rounds before he sticks you. There's about a 90% chance he'll stick you at least once if not more and kill you. When I got to be a "knife wielder", I bowled almost everybody over and "got" them. Convicted felons in our prisons practice knife work and gun disarms when the C.O.'s aren't watching.