Never let a ball go down the middle of the court without someone putting a racquet on it. Anytime the ball is hit wide I instruct my teams that both players must flow in the direction of the ball with the ball side covering the alley and the partner overplaying the middle. Do not let them have an open shot down the middle. If the opponents win the point with a great crosscourt angled shot fine, but my teams are in big trouble if the winning shot went down the middle unmolested.