C'mon, choke me!" barks instructor Darren Levine to one of his students, a wiry lieutenant with the Los Angeles police department. The officer obliges and pays the price. Lightning fast, Levine breaks free and delivers a kick to his opponent's groin. The officer doubles over, only to be greeted by a sharp knee jab to his face. While the exercise is a simulation, Levine's students are nonetheless wide-eyed.
"When you're fighting for your life," Levine, 38, tells his class, "you've got to be as fast and as fierce as a wild animal. Your only goal is to save yourself using whatever...