This drill enables you to work on leg strength, endurance, footwork, body control, and speed. All you need is one half of a tennis court and three tennis balls.
To set up, place the three tennis balls in the left alley about 1 foot from the net and spaced apart by about 4 inches in a line. A clay court works best. This allows you to make a grove in the clay in which the balls can rest.
To perform the drill you first align yourself on the baseline ready to sprint down the alley towards the three tennis balls. Your stance prior to starting should be in a low split step position. (This is referred to as the Athletic Position.) You begin by sprinting towards the tennis balls. Once close to the tennis balls drop into a split step position, squat down and pick up one ball. Then do a crossover step with your left leg and continuing to shuffle towards your right along the net. Once in the other alley freeze for a second in a low split step position. Then, back peddle up the alley. Once you have crossed the baseline drop into another low split step and freeze it for a second. At this time toss the tennis ball back into the corner behind you out of the way. Then, do a crossover step with your right leg and continue to shuffle to towards your left until you reach your original starting position. (Both of your shuffles should be done in a low position covering plenty of ground per shuffle in a powerful manner.) You repeat this sequence for each ball remaining. Then, repeat the drill again with the balls in the other alley. Once you have done this you have completed the drill.
The 4 Corner Box Drill is a very challenging with three balls. This drill will exhaust the muscles in the legs if done properly. The most challenging feat is to remain in a low stance when shuffling along the net and again on the baseline. As you fatigue you will want to stand up in a more erect position. However, this drill forces you to fight against this desire. The goal is not to beat a clock. Rather it is to work on the technique used in a short sprint, shuffling, maintaining a low athletic position, and one’s ability to focus when in discomfort.
Master this drill on both sides. Then if you are able add a fourth ball.