Undefeated in seventy-one fights, Bobby Gunn, 42, is the undisputed world champion of bare-knuckle boxing. He rules the circuit, a nationwide underground network of pro boxers, mixed martial artists, and anything-goes street brawlers who square off without gloves in empty warehouses and mobster McMansions for as much as $50,000 a fight. It’s dangerous, bloody, and illegal almost everywhere—a secret world run by organized crime. And for Gunn, a devout Christian using the prize money to put his seven-year-old daughter through private school, it’s his only shot at a better life—one that may even revive America’s first sport in the process.