This one is for training a back how to make the correct call. It can be done with three or four people. Two players defend a court, including the back who is being trained. The other player(s) will be throwing attacks.
One of the offensive players will be throwing leads, and the other will be throwing attack shots. The leads should be flat backhands, since they are easy to read and to tip if necessary. The offensive players should throw the following attacks in sets of five:
Repeat the above sets until the back is becoming comfortable making calls and escaping. At that point, stop announcing what the timing will be, and have the back practice recognizing the timing on his own. Making the right call consistently will take a lot of repetition. As the back gets better and better, you can start varying the style and difficulty of the attack (steeper leads, dump attacks, different lead shots, etc).
This drill is designed for three people. Each person takes a turn as the attacker. In the attacking court, place a marker at midcourt, and one halfway between that one and the front line. The attacker gets five attacks from each of those two marks, and five from the front line. Keep track of the points scored by the attacker after the fifteen attacks. Rotate to the next attacker, with the remaining two defending their court.