In 1999, after a series of wildly adventurous jobs around the world, Sam Sheridan found himself in Australia, loaded with cash and intent on not working until he'd spent it all. It occurred to him that, without distractions, he could finally indulge a long-dormant obsession: fighting. Within a year, he was in Bangkok training with the greatest fighter in muay Thai (Thai kickboxing) history and stepping through the ropes for a professional bout. That...