GUEST is right: for some it's training.

That's why I'll run from a potential fight. Once upon a time, I taught this stuff. Those of use who did never even got into horseplay -- too much possibility of slipping into "finishing techniques" and you feel so lousy after killing someone unnecessarily. Just ruins your day.

(PS: I was trained to hurt people with my hands, knives, guns, explosives, and combinations and improvisions thereof. Those who know don't.)