sentences:  Because players receive points for fouls by their opponents, repeatedly snookering one's opponent is a possible way of winning a frame when potting all the balls on the table would be insufficient to ensure a win or tie.This portion of the frame is known as the "snookers-required" stage.A free ball is a player-nominated substitute for the ball "on" when a player becomes snookered as the result of a foul committed by the opponent.