Set up in groups of 10, with 1 ball and post.
4 players stand in a line, with 3 players in a line in front filling the gaps.
The feeder takes their arm back (as though they were about to bowl), and the back line moves forward to the front. The feeder then releases the ball and the fielders either catch it, or field it back to the feeder or post (ball can be thrown, rolled or bounced).
This practices walking in as the bowler is bowling, and the importance of backing up (players who are walking in practice catching on the move, whereas the non-moving players practice backing up).
Having a set position to catch with catching hands ready.
Rotate players regularly to give everyone a chance to catch and back up.
Introduce a runner to put pressure on the fielders.