Originally developed in Canada in 1977, wheelchair rugby is a competitive game in which two teams of four players in wheelchairs attempt to maneuver the game ball over their opponent's goal line while in possession of the ball. It is an exciting game with aggressive players and fast-paced action. Offensive strategies are designed to exploit defensive weaknesses. Defensive strategies involve blocking, forcing turnovers and intercepting or batting away the ball from the offensive team. Wheelchair rugby is an official sport of Wheelchair Sports USA (WSUSA) and the Paralympics and is played primarily by individuals who have quadriplegia. Other eligible players include those with cerebral palsy or with post-polio. There are approximately 50 teams throughout the United States.