#1 stays in the middle and puts on an active straight up force. #2 and #3 stay in front of their players and discourage passes that gain metres up the line. #4 and #5 plug the gaps to stop passes to defence's #4 and #5. #6 is an active short deep discouraging the over the top throw and putting additional pressure on any mid to long throws. #7 is the deepest and discourages the deep throws.
If offence move the disc to the side #1 doesn't follow. Whoever is on that side forces middle. #5 as the plug wants to discourage the throw up the side line. and #6 covers the throw to the middle.
Little passes that gain a metre or two are okay, the idea is to make them throw sideways so much that an error is forced or for them to take a risky throw over the top.
If they swing it, and offence comes forward, the plugs need to cover that pass and the side defence needs to force middle quickly.
If they get the pass up the field through the middle, #4, #5 and #6 don't put a mark on and shuffle back to stop any continuation.
#6 covers the middle here to discourage the throw to #5.
The dump pass to #2 is okay as long as it's backwards or sideways, we don't want #2 to cut up the line and gain a wide open throw to the deeps.
#4 can cover that while #2 keeps the mark on.