A sustained exchange of shots after the serve. A rally can be two shots or fifty. The longest recorded rally in professional tennis lasted 643 shots. Long rallies test endurance, consistency, and tactical patience. Short rallies mean someone's dictating play aggressively. The crowd starts getting into it around the fifteen-shot mark.
"Thirty-shot rally. Both players digging in from the baseline. Finally she finds the drop shot. The crowd is on their feet."