Chef Marc Vetri likes to fight. "As a chef you have to have an outlet to let off some steam," he says. Nearly two years ago, Mr. Vetri took up Brazilian jiu-jitsu, a mixed-martial art that focuses on ground fighting and self-defense. Within two months he persuaded two of his chef/business partners to join him. Now, even some of his line cooks show up for Saturday morning fight sessions. "The workouts have become a bonding thing for the guys," he says.

Mr. Vetri, 45 years old, oversees a mini Italian restaurant empire in Philadelphia...