Playbooks

Y Seam out of Shotgun Spread Y-Slot lines up two receivers to the left, a tight end and running back to the right. The left side runs a post from the outside receiver and a corner route from the slot after crossing underneath, while the tight end (Y) attacks the seam vertically up the middle of the field and the running back releases on a flat route to the right as the checkdown or man beater against a blitz. The primary read starts with the Y seam route working against linebackers and safeties in zone drops, then progresses to the post-corner combo on the left if the safety bites down on the tight end or if you get man coverage across the formation.
Watch the middle linebacker depth at the snap, if he sits shallow or bites on the flat the seam route will split the zone cleanly. Identify single high safety shells presnap, since Cover 3 and Cover 1 struggle to get a defender over the top of the seam in time. Post snap key the safety over the tight end, if he stays flat footed reading the quarterback the seam throw is live immediately after the snap. Cover 2 and Cover 4 shells with safeties sitting deep and outside will squeeze the seam window, forcing you to work the post-corner combo on the backside instead. User controlled linebackers who spy or lurk the middle of the field can undercut the seam route, so look off the throw or use pump fakes to move that defender.
Presnap identify if the safety is shaded over the Y or sitting in a two high shell, since a single high look opens the seam immediately.
Hot route the running back into a wheel or option route if you expect man coverage so you have a answer against a linebacker matchup out of the backfield.
Use this on second and medium or third and short where the seam window against zone defenses is still available before linebackers can sink deep.
Pair this with 45 Quick Base or RPO Peek Slant earlier in a series so defenses respect the quick game and open up the intermediate seam shot.
Against aggressive user blitzers, get the ball out fast to the flat route since the running back becomes your answer versus pressure looks.