Who decides number of players in a rugby lineout?

The number of players in a Rugby lineout is determined by the teams involved in the match, specifically based on their strategy and the rules of rugby. Each team can choose to have a varying number of players participate, but typically, a lineout consists of players from both teams forming two lines of players. The exact number can also be influenced by the specific laws of the competition being played, which may set a minimum or maximum number of players allowed in the lineout. Ultimately, it's a tactical decision made by the team's captain and coaching staff.