sticking the nut

Have you noticed that skull-crashing is catching on in the movies? In the 2005 Wes Craven thriller Red Eye [warning: mild
spoiler follows] the villain (Cillian Murphy) deliberately crashes his skull into the forehead of the leading lady (Rachel McAdams),
sending her into unconsciousness. Later, she crashes her skull into his forehead, and this time he's the loser. My question is,
in real life does anyone deliberately do this skull-crashing business? How do you know, when you crash your skull into someone's forehead,
that you will stay conscious while they fly off to la-la land? -- John Hollenhorst, Salt Lake City

SDSTAFF Gfactor replies:

First of all, John, it's not usually called "skull-crashing" -- the practice you're referring to is typically known as head-butting.
And yes, sometimes people really do engage in it.

The most widely witnessed real-life head-butt in history was almost certainly the one given by French soccer star Zinedine Zidane to
Italy's Marco Materazzi during the 2006 World Cup finals. Materazzi later admitted he had provoked Zidane, and both players were disciplined.
In a 1992 New York Times article, Morgan Gendel reported that soccer players in the northern British Isles called the maneuver
"sticking the nut," and that it was a "street-fighting move popular mostly in working-class sections of Britain and Ireland."

Of course, head-butting is unwelcome in most sports, even those directly involving combat. A head-butt motion shows up sometimes in
the traditional sequences of karate moves known as kata (there's one at about 1:21 in this clip of the kata called Gojushiho Dai),
but head-butting an opponent is off-limits in competition.