In my limited time playing tennis for school and ping pong in my free time, I've learned how to properly return a fast serve. I would always see a quick serve coming at me and be tempted to swing hard back at it, but that would always end in the ball soaring off to either side. My coach instead told me to just hold my racket still and steady and let the ball bounce off of it. This technique has a lot of physics behind it that makes sense. Think of a ball being bounced on the floor. The floor does not swing at the ball to propel it back to your hand, rather the ball merely hits the still floor and goes back up. This can be thought of an elastic collision where all of the potential and kinetic energy of the ball is conserved causing the ball to bounce back up to one's hand. Similarly in tennis and ping pong, a fast serve met with a still racket causes the ball to go across the net with the same speed as it was served with but in a controlled manner. Therefore, even though swinging at the ball will cause its speed to increase, to get a fast AND controlled return, one should cause and elastic collision with the ball and the racket by holding the racket steady and still.