Racquetball is a game for two or four players, played in a 4-walled court, using short-handled rackets and a small rubber ball.
Julian Bashir was the captain of the Starfleet Medical Academy racquetball team in 2368. His team won the Sector Championships in his final year. He played against a Vulcan in his final match, however, he found his greatest opponents were the ones with no formal training. At another tournament, he picked up a 5,000-year-old battle warm-up exercise from a top player. According to legend, the warm-up makes the heart a friend to the hand. (DS9: "Rivals")
In 2370, Miles O'Brien built a racquetball court aboard Deep Space 9. (DS9: "Rivals")
After two months of Keiko O'Brien's absence in early 2371, Miles O'Brien and Julian Bashir had played 70 games of racquetball. (DS9: "Fascination")