Racquetball is a sport played with racquets and a hollow rubber ball on an indoor or outdoor court. It was invented by Joe Sobeck in 1949 incorporating rules from squash and handball. Unlike many other racquet sports, the walls, floor, and even ceiling of the racquetball court are considered in-bounds. The game is normally played by two players, though there are variations with three or even four (which can get very crowded). Two player games are called singles, three player games are typically called iron-man (2 on 1 during entire game) or cut-throat (each player take turns serving to the other 2), and four player games are called doubles.