When the player marking the dump (3) is on the open-side of the pitch, he poaches upfield to stop any upfield throws.
OH
SHIT DOE
Eventually the handler will look to swing it to the free man (3), here's where the communication is important.
The poacher (3) needs to recover ASAP, re-establish the force.
GET
FACKED
HOWEVER (back to step 4) - If the handler swings
...and then proceeds to attempt to give-and-go by cutting upline, the poach (3), needs to tack initiative and call that switch.
"Oh shit!" says #3. "DIT are just too good" he screams, throwing a stall 9 callaghan