If a drop volley has a reasonably low trajectory, its quality can be measured fairly accurately by how many times the ball bounces before it reaches the service line. Three bounces is generally considered the minimum for a good drop volley, but it's possible to get many more, to park the ball inside the service box, or even to have the ball bounce back to your own side.
In the Drop Volley Contest, each player gets six balls fed so that she'll meet them below the top of the net. Her goal is to make each ball bounce as many times as possible before the service line (or its extension). She gets one point for each bounce, but because a ball that rolls, parks in the service box, or bounces back to the hitter's side is essentially equivalent to an infinite number of bounces and would thus ruin any arithmetic, we stop counting at seven bounces. A shot is disqualified if it reaches a height greater than six feet above the ground, because even if such a drop volley were very short and well spun, its height would make it too easy to run down. Each player takes a turn hitting six drop volleys in a row to earn a total score between zero and the maximum possible, 42.
It's usually best to feed only to one side (forehand or backhand) per turn. Some players may need a turn or two to start to get a feel for the shot, so doing multiple rounds makes the drill more likely to produce improvement.
Difficulties: Feeding a ball low enough to be appropriate for a drop volley gets more difficult as you feed from farther back. Feeds from farther back also have more pace on them, which makes them more difficult to drop volley. It's usually best to start off feeding from inside the service line, and then in later rounds, if players are ready to handle more pace, feed from farther back.
