Well, it’s effective in movies because it *looks dramatic and entertaining*. If you want your bad guy to seem really tough, have him hit people with his *head* instead of his fists! If you want to show how determined your hero is, have him escape from a bear-hug by head-butting his enemy!
Like a lot of fighting in movies, what *looks entertaining to an audience* is very rarely what’s actually effective in a real-world fight.
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