The Half Volley
This shot requires more perfect timing, eyesight, and racquet work than any other, since its margin of safety is smallest and its manifold chances of mishaps numberless.
It is a pick-up. The ball meets the ground and racquet face at nearly the same moment, the ball bouncing off the ground, on the strings. This shot is a stiff-wrist, short swing, like a volley with no follow through.