The 2nd player in the line throws a high ball over the head of the 1st player, for them to run onto and catch close to the bowling square.
Once they have caught the ball they should turn and throw to the fielding player at the 4th post.
The 4th post player then throws the ball to the new 2nd player in the line who then repeats the exercise.
Players move onto the next position so that this drill rotates continuously.
The player that runs out for the catch runs to the fielder's position after throwing the ball and so on...