Underground calisthenics battles are exactly like UFC meets a rap battle — 150 people crowded around a circle, fighters walking out with masks and chains, nicknames like 'Extra Money' vs 'Calisthenics the Prince,' and people throwing money and betting. The battle set: 100 burpees, 50 muscle-ups, 75 dips, 75 squats with a 65-pound dumbbell. This is the next big spectator sport.