This set piece within a game is used to restart play once the ball has gone off the pitch.
The official formation of a lineout is when two players from each team arrive at the point of line out. Once the lineout is formed, the attacking team can decide on the number of players to take part in the line out. The defending team must match their number of players.
There must be a 1 metre gap between the two teams. Usually there are 7 players in the line out and a hooker. The hooker in the attacking team throws the ball in to the line out, and the hooker on the defending team must stand in the 5 metre channel.
In the line out you have two lifters that lift one player when the ball is thrown in. The players in the air cannot touch or grab each other. The ball must be thrown straight and if not the opposing team has a choice of either a line out or a scrum to restart play.
Once the team has won the ball, it is usually thrown to player 9 and play resumes.