We are red and we are on defence. Player R1 is on the mark and stall counting. R2 and R3 are in the 'cup'. R7 (deep) communicates with R4,R5, and R6 (mids).
At high stall count, R1 can stand on the extreme around to make the back-field swing (to B2) difficult. R2 can also shift slightly to prevent the throw to the other handler (B1)
If they swing the disc, the mids are responsible to stop the continuation throw. in this case, b4 is the most dangerous one. So make sure R4 is tight on B4.
The cup needs to catch up with the disc as quickly as possible.
So now B4 has decided to go to the other side. R4 should leave B4 and warn R5.
Sometimes offence might 'crash' into the cup. The mids/anyone else should shout 'crash' to warn the people in the cup. R2 can try to prevent the pass.
If the crash failed and the disc was swung back to B3 instead, R6 must be EXTRA alert to stop the continuation to B4. This is especially important because the cup takes a while to catch up. R3 & R2 can look behind briefly to check if there's any danger behind them before closing into the cup.
However, If the disc is successfully thrown downfield, R6 should again prioritise stopping the continuation to B5 instead of marking B4. This is what people mean when they shout "drop! drop!" The cup should now try to catch up.