This defensive play is to be used once the offence has made it past your brick mark and are looking to score. When the"WALL" or "FLOOD" call is made, four players line up on the endzone and one remains out as chase.
The chase will ALWAYS force backhand, no matter where the disc goes.
The chase's main role is to harrass the handlers, force them to throw many times and eventualy cause a turnover.
The players in the wall will attempt to block throws to the offensive players in the endzone.
They will likely keep moving form one side to another, so the wall needs to communicate so that all gaps are covered and everyone knows where the opposing players are. The sideline will be useful in this regard.
It will be important to ensure that no offensive players become too free at the back of the endzone, as an overhead score will be relatively easier. Wall players can step backwards to menace these throws.
The overall aim of this tactic is to force so many throws that a drop/throwaway/block becomes more statistically likely.
If the chase gets tired they can switch with someone in the wall if necessary.
Playing against a good wall is very frustrating! Even if after a long time they do score it could potentially make them rush their O points in future.