Select between 2 to 6 people to be in the middle (depending on the size of the group). The rest of the group each have a ball and on the command they have to dribble from one end of the court to the other. They have to make sure that they avoid the catchers in the middle who are trying to knock their ball away.
If one of the dribblers is caught they join the other catchers in the middle.
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.