Abstract: The size of a walled ball-court's playing area is changed by moving a wall into and out of one side thereof (e.g., the end of an elongate court). The wall moves on wheels rolling in horizontal tracks inset into the floor of the court. The movable wall is mounted on one end of a frame extending outwards from the ball-court, and the weight of the wall is balanced with counterweights so that the wall does not tip when moved. A mechanical drive, which may be manually powered by a single operator, applies horizontal forces to the wall in order to move it back and forth along the tracks. In a preferred embodiment, two sets of wheels, spaced out along the movable wall, are used. In this configuration the spacing between the two sets of wheels is adjustable to allow an installer to select an optimal spacing.