Sport on TV: McKenzie feels weight of the world on his shoulders

If there was an Olympic medal for fighting outside pubs at closing time, Britain would definitely be on the podium, as a million visitors to London may be about to find out. Yesterday saw the Olympic debut of Ashley McKenzie in judo, and he has been in a few scrapes away from the mat as Bad Boy Olympian (BBC4, Tuesday) bore witness.

In a week in which Auntie Beeb has eulogised the golden boys and girls of the Games, with gushing portraits of the utterly charming Tom Daley and Victoria Pendleton, the inside story of an athlete who suffers from Attention Deficit Hyperactivity Disorder provided a fascinating change of pace, like veering off into an Olympic traffic lane. In McKenzie's case, one with few stop signs or red lights.

There have been Olympic bad boys aplenty since Ben Johnson in 1976 – and enough bad girls who looked a lot like boys. But McKenzie is one of the few who cannot take drugs that would enhance his life because the medication for his illness contains substances banned because they would enhance his performance. As if his condition did not make his ambition to be the best in the world hard enough already.

McKenzie is certainly hard enough, as we see on the last night of the Team GB training camp in Barcelona when he goes out to celebrate his 23rd birthday, walks up to a stranger outside a bar and announces: "I'm gonna smash your face in." His coach, Chris Bowles, has a fight on his hands trying to control his charge, having been handed the baton of caring for Ashley from his mother in the run-up to the Games. "What I tend to do is take a step back," he confides, and that sounds like good advice. He in turn has let go his grip when McKenzie is in the clutches of the Team GB management.

But for all Bowles' exasperation, McKenzie goes from the camp to the World Cup, the last event before London 2012, and wins his weight division. Perhaps he exemplifies the old spirit of the Olympics in more ways than one. Not only does he show that anyone can aspire to be the best in the world regardless of the constraints holding him back, but also that you can still compete after a late night or two, in contrast to all the other highly professionalised athletes. He is more likely to be wrapped in bandages than cotton wool.

Like so many stories in sport, judo has had a beneficial effect on the wayward youth who was placed in a psychiatric unit by his mother at the age of 11. He describes what the martial discipline does for him: "I'm not the tallest guy so it gave me the Yellow Pages to stand on to kiss the girl. I'm on the pavement, not walking in the road." It may not be a road paved with gold, but even though he became the first Brit to be knocked out of the Olympics after only 250 seconds, it is surely taking him in the right direction.

One note of caution. When McKenzie visits his father's side of the family, he is regaled with advice from a Rastafarian uncle with dreadlocks down to the floor and a profusion of spliffs on the go. Too much time spent in that foggy room and the drug-testers will be banging the door down. Not that a few puffs on a joint will do him much good in the midst of a judo match. The dreadlock is a far cry from the armlock.