2018 USPA Rules
Rule 20- HOW PLAY COMMENCES
b. If a player is on the wrong side of the line-up when the ball is thrown in, he may not make a play until he is behind a member of his own team who was properly positioned when the ball was thrown in. Should he make or attempt a play prior to being passed by a member of his own team who was properly positioned when the ball was thrown in, a penalty shall be awarded. If all four players on the same team are on the wrong side of the line-up when the ball is thrown in, no player on that team may make a play until play is interrupted and resumed. If any such player makes a play, a Penalty 2 shall be awarded to the other team.
c. During the throw-in, the Right of Way will be established when the ball leaves the line-up. Until such time, players may play the ball from any direction or angle providing they do so without creating danger or a risk of danger to themselves, other players or horses.