Middle closed / middle open

The quarterback's first question on every snap: is the middle of the field closed or open? One safety deep in the middle means closed (MOFC — the Cover 1 and Cover 3 family) and the deep middle is occupied, so the answers live outside and underneath. Two safeties deep means open (MOFO — Cover 2, 4, and 6) and the deep middle is vacant, so the seams and the post come alive.

Read one, every snap — before corners, before the box count, before anything. It cuts the coverage menu in half.