What is Bobby's fatal flaw in the novel, Flesh and Blood?

Bobby's character, formed, in part, by an education in the mean streets and bolstered by rage at his father and a passion for his mother, is marked by a fatal flaw which, like Achilles, Cuchullain, and the nameless berserkers of the Anglo-Saxon epics, engineers both triumph and defeat. He flies into a murderous rage when he fights, a primitive survival mechanism which prematurely ends his amateur career and propels him, unschooled, into the big time before he is ready: "something else was happening: sound was coming out of me, the wild crazy screaming anger, high-pitched against the deeper darker roar of the crowd."