Playbooks

Four Verticals out of Shotgun Doubles Flex sends both outside receivers straight up the field on vertical routes to stretch the deep zones sideline to sideline, while the slot receiver runs a seam route up the middle of the field between the safeties. The running back releases out of the backfield on a checkdown route up the numbers underneath the seam, giving the quarterback a built in safety valve if the verticals are covered deep. This is a classic Cover 2 and Cover 3 beater, with the primary read progression starting on the seam route to see how the middle linebacker and safeties react, then working outside to the vertical routes based on which cornerback or safety opens up first.
Pre-snap, identify if the defense is showing two high safeties or a single high safety, since Four Verticals is designed to punish both shells differently. Watch the middle linebacker depth at the snap, if he sits shallow the seam route will be open behind him for an explosive gain. If the safeties bail deep immediately post-snap, expect a Cover 3 shell and target the seam or the vertical with the most inside leverage. User controlled lurk defenders sitting in the deep middle can rob the seam route, so have a plan to work the outside verticals or the checkdown if that defender squats. Man coverage on the outside with press alignment is difficult to shut down completely, but a physical corner press disrupting release timing can slow down the vertical stems and force the quarterback to hold the ball longer.
Attack single high safety looks and Cover 2 shells where the safeties have to choose between the two outside verticals and the middle seam.
Use pre-snap motion or a hot route on the running back to swing him into the flat if you see man coverage and need a quick outlet against a blitz.
Against Cover 3, target the seam route first since the middle of the field defender has to cover the deepest third alone and can be stressed vertically.
Best called on second and long or third and long when you need an explosive gain over the top, but keep it in your pocket on early downs to avoid predictable shells.
Pair this with a play action rollout or a quick game concept from the same personnel to keep defenses honest and disguise your intentions before the snap.