A full rugby union scrum contains eight players from each team.
The eight forwards bind together in three rows. The front row has two props and a hooker, the second row has two locks, and the back row has two flankers plus the number eight. Together, these players form the pack that contests possession after certain infringements or stoppages.
The scrum-half feeds the ball into the scrum but does not become one of the eight players in the formation. The two packs push against each other while trying to win or retain the ball with their feet.
A team may use fewer than eight players in a scrum after a player is sent off or injured, depending on the applicable laws and competition regulations. That exception does not change the standard full-strength formation: eight forwards per side.