Player battle drill where player one is trying to exit up the boards and player 2 is trying to stop them.
Progress to 2 on 2. With 2 on 2 the important point on D is no space and use your body, on forward, quick decisions and getting open.
Other Side
1 on 1, 2 on 2 and 3 on 3 depending on what the coach calls. Same thing when more than 1 on 1. Anticipate, get open, keep moving.