The most basic shell emphasizes positioning and communication. "Shell" provides latticework for us to build more complexity. It demonstrates defense on the ball, one and two passes away.
We increase the degree of difficulty by adding individual passing and cutting (to deny the give-and-go) or passing and screening (on or off the ball).
Shell principles teach help and rotation.
Coaches increase the degree of difficulty by adding 'advantage-disadvantage' elements.
As players become more experienced, they learn to "tag" cutters going through the defense.
Sixers' coach Brett Brown walks us through shell drill and principles:
2) Pass and defend pindown
3) Pass and cut through
4) Corner drive with help
5) Top drive with help from away to protect corner 3
6) Live offense/defense
"no post, no pick-and-roll" during the drill