Welcome to calcio storico, a centuries-old competition in Florence with very few rules and the sort of human wreckage generally associated with the gladiators. Last Tuesday, about 24 hours before he jammed his fingers into another man’s nose, dropped his elbow across another man’s neck and put another man’s feet where one’s ears are supposed to be, Rodrigue Nana considered, just for a moment, the basic notion of fear. “Do you want to know what I am afraid of?” he said, his fingers tracing the meaty scar above his left eyebrow. Nana, a Cameroon-born transplant to Italy, leaned forward, as...