I would just stick to using the term racket speed. Technically correct and easy to understand. The physics explanation (if interested) is as follows. Angular momentum must always be conserved unless additional energy is added (which is not happening here). Angular momentum is the product of mass, velocity, and the radius of the arc. The mass isn't changing, so we don't have to worry about it here. Therefore, if you shrink the radius, you increase the velocity. Thus, more racket speed.