Head-butts in football are bad. They are dangerous and can smash noses and cheekbones. Kids, don't try them at home.
Sometimes, though, did the recipient have it coming?
The politically correct answer must be, 'No.' Head-butts are so violent that they can never be condoned.
But they can sometimes be explained.
Football's most famous head-butt was understandable.
Marco Materazzi made Zinedine Zidane see red in the 2006 World Cup final by insulting his sister. France's captain responded with his head-butt to the Italy defender's chest that sent shockwaves around the world. Of course, Zidane shouldn't have melted down. But given how Materazzi provoked him, it's not hard to fathom out why he did.
The same goes for Marouane Fellaini.
The midfielder from Belgium with an impressive shock of hair recognizes that he shouldn't have head-butted Ryan Shawcross. But given how the Stoke defender crawled all over the Everton player when their teams met in the English Premier League, it isn't wholly unsurprising that Fellaini did a Zidane.
The laws of football are clear: Players aren't in theory allowed to wrap their arms around an opponent to stop them getting the ball or taking up a good position. They are not meant to yank shirts and arms. The rules say referees must "deal firmly" with holding offenses, especially in front of goal.
Yet these anti-football tactics are systematically used. In match after match, grappling players turn penalty areas into a WWE free-for-all.
One answer would be to copy UEFA and station additional referees next to goalmouths. The European football governing body believes that having those extra two pairs of eyes in its matches has cut down holding and shoving and given attacking players more chances to reach the ball.
But another answer would simply be for referees to be less tolerant, to apply the rules that already exist. Too often, pushers and pullers aren't punished. Little wonder they keep coming back week after week. And perhaps logical - however reprehensible - that Fellaini ended up taking the law in his own hands.
At various times in the match that ended 1-1 on Saturday, Shawcross did everything he could to blunt the threat posed by Everton's leading league scorer this season. He shoved and blocked Fellaini from running in the penalty area. He wrapped his right arm around his back and used his left to grab hold of Fellaini's arm. He wrapped both arms around Fellaini in a bear-hug. He wrestled his shoulder.
In the 59th minute, Fellaini lost his cool, delivering his head-butt into the face of the octopus in a red and white jersey. Shawcross fell to the ground clutching his cheek but wasn't badly hurt. For his sin, Fellaini is banned for Everton's remaining three games of 2012 - against West Ham, Wigan and Chelsea.
"There was a lot of pushing and pulling going on inside the Stoke penalty area and I didn't feel I was getting any protection from the officials," Fellaini said in a statement. "I have no excuses, I was disappointed with the way I was being treated and I lost my temper, which was unprofessional of me."
Fellaini has had it both ways this season. At Manchester City on Dec. 1, he was the one doing the yanking. He pulled down Edin Dzeko in the box. Referee Lee Probert awarded City a penalty. Which begs the question: Why isn't pushing and pulling always punished?
"There's just no consistency," said Fellaini's teammate, Sylvain Distin.
Holding isn't a new problem, just a recurring one. In the 2006 World Cup final, the verbal spat that escalated into Zidane's head-butt started with Materazzi holding the France No. 10 in Italy's penalty box, standing behind him, his thick tattooed left arm clutching at Zidane's chest, preventing him from moving freely for Florent Malouda's cross.
Zidane and Materazzi exchanged words, then the France captain wheeled around, lowered his head and rammed the Italian in the chest, knocking him to the ground. Like Fellaini, Zidane was banned for three games but served the punishment by doing community work because he retired from football after the final.
Gary Neville, the former Manchester United defender and now the most lucid and convincing football pundit on British television, opined that pushing and shoving is simply part of the sport and that Fellaini was at fault for reacting so violently to it.
"It's almost been made out to be Stoke's fault, like they're the sinners because Ryan Shawcross is holding," Neville said on Sky Sports. "This goes on all over the pitch, every single game, arms in the air, physical challenges. It's just the way the game is."
"To me, that's just competitive," said Neville.
Football is a contact sport. It should be physical. The job of defenders is to defend. But football can do without the sly shirt-pullers, bear-huggers and arm-tuggers with clinging tentacles. By clambering all over attacking players, they deny fans spectacle. Football mustn't become rugby.
Head-butts should never be the answer.
But there are sometimes reasons for them.