wrist. The stop-volley has no wrist at all.

Use all your wrist shots, chop, slice, and drop, merely as an
auxilliary to your orthodox game. They are intended to upset your
opponent's game through the varied spin on the ball.

THE HALF VOLLEY

I have now reached the climax of tennis skill: the half volley or
trap shot. In other words, the pick-up.

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. The racquet face travels along the ground
with a slight tilt over the ball and towards the net, thus
holding the ball low; the shot, like all others in tennis, should
travel across the racquet face, along the short strings. The
racquet face should always be slightly outside the ball.

The half volley is essentially a defensive stroke, since it
should only be made as a last resort, when caught out of position
by your opponent's shot. It is a desperate attempt to extricate
yourself from a dangerous position without retreating. NEVER
DELIBERATELY HALF VOLLEY.