The playing elbow is the elbow on the arm that the player holds the racket with. A common strategy is to aim an attack (like a loop kill or a smash) at the playing elbow of the opponent (this is more effective against shakehand grip players). The elbow is the point between the forehand and backhand, so the receiver must quickly decide whether to use the forehand or backhand, often resulting in a hasty decision and a weak return. If you aim at the forehand or backhand sides, you can expect a counter attack.
Coach Wiki Article / Falkenberg Drill