One player is at the net, ad side; the other player is at the baseline, ad side.
Players rally cross-court (net player volleys, baseline player hits backhand ground-strokes) having the baseline player alternate between slice (under-spin) and topspin.
It is not a competitive drill – just rally and practice.
Do the same from the deuce side where the baseline player practices slice and topspin forehand groundstrokes.
Players can switch roles (the baseline player comes up to the net while the net player moves back to the baseline).