Flub

Flub requires massive amounts of FOCUS

Flub is all about focus-focus-focus. Initially I was going to recommend this for higher level players but I think I have a way to make it work for anyone.

Flub is easiest to manage with four players. If you have more and need them to rotate positions frequently, that ratchets up the focus component. They must remember where each position is expected to hit to.

Four players take the court, two at each baseline. Each of the four playing positions is assigned a number, letter, or color. Let's say for this example we use 1, 2, 3, and 4. Player 1 drop feeds or serves to Player 2. Player 2 hits to Player 3. Player 3 hits to Player 4. Player 4 hits to Player 1. Pattern must not be altered. You will find the butterfly pattern useful here:

• Server/1 feeds/serves cross court to 2. 
• 2 hits straight ahead to 3. 
• 3 hits cross court to 4. 
• 4 hits straight ahead to 1.

Scoring: all players begin with a set number of points. Any player making an error either in execution or target loses a point. At end of playing period, player retaining most points wins.

Variation
Too hard - have players tossing ball rather than hitting with racquet.Too easy - I can't think of any group of players that would find this too easy, but if you must make it harder, have players rotating positions after every point, even rotating 'Around the World' to the other side of the court.
Multiplayer rotation - rather than deducting points on errors, have players making errors replaced with waiting players.

Adapted from The Tennis Drill Book by Tina Hoskins