Assign players as per the diagram and assume starting positions. [C] has the ball.
To start, we'll demonstrate double defence on the opposition [GS], who has proven to be really hard to stop. There are 2 main ways to double defend - both involve "sandwiching" the player between 2 defenders.
a) Stand left+right of the [GS], slightly staggered so one defender covers straight leads, the other covers dropping back
b) Stand directly in front+behind the [GS]
Other players help out by:-
Sagging in front of the [GA]
Feeders play deeper to limit the space of [GA]
Don't allow [GA] and easy shot by being responsive when double defending. Take a step towards [GA] if they've moved to a dangerous scoring position.
Repeat several times, starting from different points on the court.
Now let's practice double defence from an opposition centre pass, as follows:-
[C] drops back to double defend the [WA] instead of pressuring the opposition [C]
As soon as the first pass is complete, [C] must scramble to cover the opposition [C], to avoid a double play.