Passing on some defensive drill information from notes at an coaching clinic in Las Vegas a couple of years ago with Bobby Knight. I like the idea of putting the defense at a disadvantage in drills, forces players to work together as a team:

Team Defense Drills
a. Always set a restriction (e.g.: 15 sec. shot clock)
b. Always try to put the defense at a disadvantage

1. 5 vs. 4 full court to 4 vs. 5 back
2. 4 vs. 4 with 1 extra man in each corner (“6 vs. 4”)
• 4 vs. 4 shell where corner guys can attack, defense must communicate and rotate

3. “5 vs. 5 change”
• Coach dictates when to “change.” On signal, player drops the ball and moves to defense
• Players may not guard the man guarding them

4. 4 vs. 4 with Post (“5 vs. 4”)
• 4 vs. 4 shell where Post man is pressure release
• Post has freedom to do what he wants. He can screen or look to score
• Defense must communicate and rotate to stop the post

If you're looking for more ideas for team defense and rebounding drills, you can never go wrong with Tom Izzo's DVD on Rebounding and Man Defense. Coach Izzo is the long-time head coach of Michigan State.