Sideline Cut: About 10 years ago, Mike Murphy - he of The Live Mike and RTÉ's original renaissance man - was interviewing the American writer Richard Ford on The Arts Show when the conversation took an improbable turn to the sporting outrage of the day.

It was around the time Mike Tyson bit Evander Holyfield's ear, earning himself disqualification from their world heavyweight bout and, not for the first time, global notoriety. Asked by Murphy what he thought about the act, Ford said, "Well, choose your poison."

That phrase seemed as apt as any as people all over the globe tried to make sense of the closing act in the football life of Zinedine Zidane. The Frenchman's spectacular attack on the workaday Italian defender Marco Materazzi was so explicit and fatally timed and unbelievable it instantly felt like one of those genuinely unforgettable departures from acceptable sporting conduct, comparable in shock value to Cantona's ridiculous kung-fu kick on the boorish Crystal Palace fan and the despicable body-check by the German goalkeeper Harald Schumacher on Patrick Battiston of France. It was a stunning and completely unexpected development.

Zidane repeated on French television this week that his act was unpardonable, and he asked forgiveness from the millions who had watched the World Cup final, but he was not quite contrite. He remained angry at what he insists was a dark and insidious provocation by the tough Italian centre back and indicated that he had, like the chanteuse, no regrets: he would do the same thing again.

What he seemed to be saying was that while he truly regretted such an unsavoury incident should have occurred, he was walking away from the game with a clear conscience.

Having seen Zidane in the earlier stages of the World Cup in Germany, I watched his farewell match in the jam-packed foyer of the Grand Hotel in Moate, which was perhaps not quite as atmospheric as Berlin's wonderful Olympiastadion but offered, by way of consolation, a superb half-time sherry trifle.

Needless to say, the pots of tea were left untouched for several minutes as the television flashed replays, from every conceivable angle, of Zidane's famous nod. As the maître d' observed, in what sounded like admiration, "It's a good job Zidane didn't get him in the head or he'd have broken both jaws."

That hotel was crowded with people who broke their journeys across the midlands to watch the World Cup final, still the marquee sporting event on the planet. It wasn't so much about what you would see as what you might miss. Because the World Cup is unavoidable and because Ireland is sports daft to begin with, a good few men and women seemed well acquainted with every player on the pitch. But they spoke about Zidane as if he were one of our own. And when he exacted his singular, spectacular retribution on Materazzi, one elderly woman of bingo-hall demeanour spoke for all of us when she addressed the television with, "Musha, Zidane, have you gone mad?"

A temporary loss of control was deemed the primary reason for Zidane's blow-up, and in print and broadcast around the world he was branded a disgrace. Almost a week later, that headbutt is hard to defend. But the general view that it was unforgivable, whatever the provocation, does not seem quite fair. As the saying goes, choose your poison. It seems obvious from the many slow-motion replays that Materazzi addressed the retreating Frenchman at least three times and, according to Zidane's version of events, each time he let fly with his poisonous abuse, which was possibly racist and definitely personal. Whatever he said, he managed to raise the Frenchman's fury in a matter of seconds, 110 minutes into a physically and mentally exhausting World Cup final, where only the truly great and privileged footballers get to play.

All sportspeople are used to making important decisions in a flash. When you watch Zidane stop, turn and then step viciously into Materazzi, you have to agree with his own rationale that the attack was premeditated.

It was not the consummate, professional thing to do but it was extraordinarily brave and true to his instincts.

Awareness was one of the many football qualities they say Zidane possessed in abundance. He must have been aware, even as he made the decision to lash out, that an audience of millions would be watching, appalled and fascinated that someone blessed with such athletic genius could, with the most wonderful encore just 10 minutes away, manage to destroy the memory of what should have been his night, an adieu to the football world to end all others.

Zidane knew well the lights of the universe were shining on him, and yet something in him, some combination of loyalty, street honour and competitive meanness, made him say to hell with it. His instinct told him an insult from the gutter, the kind he never let anyone get away with, should supersede the biggest show in the world. You can lambaste him for being wrong but you cannot deny it took daring. As a friend, sinking pints in Scotstown, remarked, it was a hell of a way to kill your own legend.

It might have been more palatable had he shoved or even kicked the Italian, but the headbutt has always been Zidane's retaliation of choice - as touched on in these pages with strange prescience by Tom Humphries on the eve of the final. Maybe he did not realise such a visually shocking attack would cause horror among the perfumed beau monde in the stands. Either way, that headbutt, in front of the aristocracy of world football, illuminated the harsher facts of the tough upbringing in La Castellane that has become such a celebrated part of the Zidane legend.

And it should be remembered that Materazzi was fine. He played on, nailed a penalty and led the celebrations. Zidane did not actually hurt him. In fact, we should be clear about the fact that far more dangerous and sly attacks occurred on Ireland's GAA fields over the past two weekends.

It would have been much more heartening had Zidane, ghosting in and heading what seemed to be the winning goal, gone out in the triumph and fanfare this sad old world of ours desperately cried out for. A clean, improbable, heroic triumph would have made us all feel good, if only in the heat of the moment. But it rarely works like that. Human shortcomings always, always trip up athletic perfection sooner or later.

If this sad moment teaches us anything, it is the foolishness of assuming great sportspeople can also live better, behave better than the rest of us. All but the very few fail. The most we should hope for is that they do something wonderful with the ball.

The Zidane who fired that immortal volley for Real Madrid in the Champions league final in 2002, the Zidane who held us all spellbound against Brazil a fortnight ago, was the same man who turned his back on the most glittering night imaginable. There is good and bad in all of us. As Marco Materazzi, the absurd villain in this morality play, remarked of Zidane during the week, "He has always been my hero."