This well-made documentary opens on a vulnerable moment: a good-looking young man is talking about the bones in bis nose - what's been broken, what hasn't. He is Shawn O'Sullivan, light middle-weight champion of the World Amateur Boxing Association, a teenager from the Cabbagetown area of Toronto, The Cabbagetown Kid is about his training and his devotion to his sport, culminating in his three-round bout with Cuban boxer Armanda Martinez for the World Cup in late 1981,