The second throw-in may be deep. (B) and (D) will know this as the ruckman will hold their ground immediately after the throw-in rather than run forward. (B) and (D) can now call for the ball out the
backdoor by running towards sections 2 and 4 respectively.
The same rules apply regarding the throw favouring the opposition ruckman. If (B) or (D) see that the opposition ruckman has better position, they should follow the opposition rover into section 2 or 4.
The call to the ruckman must be 'backdoor!' or similar to indicate a tap over the back.