The rules of polo are written and used to provide for the safety of both players and horses. The rules are enforced in the game by the umpires who blow whistles when a penalty occurs. Strategic plays in polo are based on the “line of the ball”, an imaginary line created by the ball as it travels down the field. This line traces the ball’s path and extends past the ball along that trajectory. The line of the ball defines rules for players to approach the ball safely. These rules are created and enforced to ensure the welfare of players and their horses. The “line of the ball” changes each time the ball changes direction. The player who hit the ball generally has the right of way, and other players cannot cross the line of the ball in front of that player. As players approach the ball, they ride on either side of the line of the ball giving each access to the ball. A player can cross the line of the ball when it does not create a dangerous situation. Most fouls and penalty shots are related to players improperly crossing the line of the ball or the right of way. When a player has the line of the ball on his right, he has the right of way. A “ride-off” is when a player moves another player off the line of the ball by making shoulder-to-shoulder contact with the other players’ horses.