1 offensive player and 1 defensive player.
The ball will be thrown up at the basket.
The defensive player must go make contact(box out) the offensive player and get the rebound.
Once the defensive player has the rebound, they pass back out to the shooter.
The drill rotation is offence to defence, the defence goes off to the back of the line.
Good team defence is five players guarding the ball, not five separate one-on-ones. The shell drill is where that starts, so here is how to teach help-side positioning and rotations from the first week of the season.
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.