The correct action that defines a throw in is : "The thrower at the moment of delivering the ball must face the field of play and part of each foot shall be either on the touch-line or on the ground outside the touch line. The thrower shall use both hands and shall deliver the ball from behind and over his head with equal force. The ball shall be in play immediately after it enters the field of play, but the thrower shall not again play the ball until it has been touched or played by another player. "
This needs to be practiced by teaching the player to go through the process that actually happens in the game. When a ball goes across the line the player who is taking the throw in must retrieve the ball, turn and scan the field for the open player/ or space to thow the ball to. This could be done by playing three players in a triangle so that when they receive the ball, they will turn and throw the ball across the triangle past the other player, in turn this player will pick up the ball, turn and throw the ball to another player---so that each time they receive the ball they are practicing the turn, the scan of the field, and the planting of both feet so that they will not be called for a foul for picking up the back foot. The power behind the throw will come with increase use of the arms over time, arching of the back and repitition.
