(A), (B) and (C) must stay at their station, which is a point on a triangle with 2-3m sides (the tighter, the easier to defend)
(A), (B) and (C) pass amongst one another, while (D) works hard to pressure the passer
(D) must have good energy and anticipation to intercept before they get tired
(D) works until they intercept, or for 30 seconds.
If you see (D) is highly fatigued, replace them
You may prefer to start with a larger triangle, then shorten the sides as a progression after everyone's had a turn.
