Set the atheletes into pairs, giving them a number.
That pair will split and go to opposite sidelines.
When calling their number, they both run in and it turns into a 1v1.
The first person to score gets a point for their team.
Make sure they all know who is on their team.
Don't limit yourself to a 1v1. Make it a 2v2 and 3v3, etc. Eventually turning into a mini game.
If they take too long, just call a 5-10 second time limit left. If no score happens, it's a draw and they reset.
Rebounding is the least glamorous thing in basketball and one of the most decisive. It is also almost entirely a habit, which means it is entirely coachable.
Good spacing is only the start. The best modern offences teach players to attack the defence's rotations and play in a permanent 4-on-3 - here is how to coach that read.
The ball screen produces almost half of all professional offensive possessions, yet most teams still teach it as a memorised play. The modern approach trains the read - giving players a framework to decide based on what the defence does, not what the coach called.