Here's a neat little offense-defense drill that CAtennis.com dreamt up last night. This a two-player drill where one player (the PARTNER) stays in the corner and moves the other player (the PRINCIPAL) around. The pattern is as follows: Shot #1 - deep forehand; Shot #2 - deep backhand (or deep inside-out forehand); Shot #3 - short backhand; and Shot #4 - short forenahd. Rinse and repeat. The PARTNER's role is to work on ball control and perfect placement. His focus is to "look good" (perfect strokes and movement) and give the PRINCIPAL a good workout.
When moving from the deep forehand to the deep backhand, the PRINCIPAL sprints forward around the cone (blue line). When moving from the short backhand to the short forehand, the PRINCIPAL circles backwards around the cone (white line). This way, the PRINCIPAL learns how to (a) hit and recover (short groundstrokes); and (b) turn defense into offense (deep groundstrokes).
After a couple of sets, the players trade roles. The point is for each player to learn how to "hit and move" particularly when the opponent has managed to push you deep off the court and out of position. Much like Aikido and Jiu-Jitsu, tennis is a moving sport where you must learn how to use your opponent's energy (offense) against them in order to gain control (and put them on the defensive).
One of the basic mistakes that players often make is to remain on the defensive when the opponent has managed to get them out of the comfort zone. They play the defensive role for the duration of the point without figuring out how to get back on top. In this drill, the PRINCIPAL learns that when he's pushed back, he can hit the ball high and deep and recover forward around the cone. Similarly, he learns how to recover backwards (in order to bisect the opponent's angle) when being pulled off-the court slightly short. By being moved out of his comfort zone, the PRINCIPAL manages to make his movement and his shots more effective and efficient under the given circumstances.