This is a drill played only on half-court… One player is at the net (inside one of the service boxes), and the other player is at the baseline, opposite sides (see graphic below).
Drill:
The net player (who has a basket of balls nearby) puts the ball in play by feeding it to the baseline player. Once the rally starts (ground-strokes versus volleys), for every ball hit over the net and inside the court the baseline player gets +1 point; for a miss (net or out) the baseline player loses a point (-1). Her goal is to get to +15 points.
All this time, the net player does not win any points; her task is to practice volleys back to the baseline player.
Players can switch roles once +15 is achieved.
Note:
This should be a cooperative drill between the two players but it can be made competitive by having the net player place the volleys so that the baseline player hustles to get to the balls.