On this Wednesday afternoon, a young boxer jumps rope. Another bangs a speed bag against the wall, sending a rhythmic pattering of triplets throughout the gym. Two fighters occupy the center of the mat, dancing back and forth in their Nikes. Their arms bob in front of their faces, searching for an opening. One seizes his opportunity, unleashing a flurry of punches. Rights and lefts, forcing spit out of his opponent's mouth when he connects. Now his sparring partner is in the corner, bracing himself on the ropes. Then he backs off.