Playbooks

Under is a play action dropback concept out of Shotgun Y Trips Wk that attacks the field with a deep cross and levels combo. The backside X runs a deep cross all the way across the field while the trips side stacks an out route from the slot, a go route from the outside receiver, and a drag from the Y that sits underneath as the checkdown flood route. This is primarily a zone beater since the deep cross and drag stretch the field horizontally at two levels while the go route occupies the deep defender, and the primary read progression starts with the deep cross before working back to the drag and out based on the shell.
Pre-snap, check safety depth and alignment since a single high safety often signals man coverage underneath, which favors the drag and out routes over the deep cross. Watch the flow of linebackers after the snap since the deep cross is designed to pull them out of position, and if they sit and stay disciplined the crosser will be covered. Identify if the defense is running a Cover 3 zone drop, since the deep cross often finds a soft spot between the hook and deep third defenders. Look for a user controlled defender lurking in the shallow zone since he can jump the drag route and bait a mistake if the quarterback does not go through his full progression. A hard blitz off the edge disrupts the play action fake, so if you see linebackers crashing downhill pre-snap, expect pressure and get the ball out quickly to the drag or out route.
Use pre-snap motion or a quick glance to identify if the defense shows two deep safeties or a single high shell before the snap since that dictates whether the deep cross or the out route will be open first.
Against zone coverage let the play action fake fully develop, then hit the deep cross on levels as it crosses the opposite hash since it is the built in home run shot on this concept.
Against man coverage the drag route from the Y becomes a quick answer versus linebackers who cannot stay in phase, so speed up your drop and get the ball out before the pocket collapses.
This play pairs well with Levels Y Out and Fl Dig from the same formation since both use similar route stems, letting you sequence plays and keep the defense guessing on which level is being attacked.
Best called on second and medium to second and long or early third down when you have time to let the deep cross develop and are not in an obvious dropback situation.