No doubt, the weakest part of my tennis game is returning hard serves. I often try to hit powerful shots, so i take a large backswing. But, when returning a serve, the ball already has a high velocity, so a large backswing is not needed to hit the ball back with a high velocity. Actually, a small swing is much more effective and accurate. This is because of the principle of momentum. When hitting a serve, a large swing is necessary to give the ball a high speed because the ball, right before contact, has a momentum very close to zero. So, a large force is needed to produce a large momentum. But, when the ball is traveling to the opponent with this large momentum, the opponent does not need to generate a large momentum in return, they only need to redirect the momentum. Thus, a large backswing is not necessary; the opponent just needs to hit the ball with a short and quick swing. If you watch professional tennis players, you will notice that they rerturn really fast serves with fast returns with a small and quick swing, as they have learned of the physics of tennis and know to simply redirect the momentum, not try to create new momentum. Once you understand the physics of tennis, you'll be looking like this guy.