Rugby is a sport played between two teams that try to score points by advancing a ball past the opposing team's goal line or by kicking the ball through a pair of uprights on the opponent's goal line. Players can run with the ball, kick it or pass it backward or sideways to a teammate. Opposing players try to tackle the player who has the ball or gain possession of the ball. There are two main versions: rugby union, which uses 15 players at a time for each team, and rugby league, which uses 13. Another version, rugby sevens, follows union rules but uses only seven players at a time for each team.