Playbooks
Seam Slot Under is a quick-hitting passing concept out of Shotgun Box Y Split with 11 personnel that attacks the middle of the field with a vertical seam route paired with an underneath crosser and a flat option. It is built as a man beater against man coverage because the seam route can win against off man or linebacker leverage, but it also holds up against zone coverage since the under route settles into soft spots against Cover 3 and Cover 2 zone drops. The primary read progression starts with the seam route to see if the slot defender gets beat vertically, then works down to the under route sitting in the underneath void, and finally checks the flat or checkdown as the last resort against tight coverage.
Identify single high safety shells like Cover 1 or Cover 3 pre-snap, the seam route becomes a strong throw if the deep safety cheats to the opposite hash. Watch for two high safety alignment indicating Cover 2 or Cover 4, in this case the under route becomes the primary target since the seam will be capped by the deep half defender. Key the middle linebacker or nickel defender at the snap, if he sprints to cover the seam and vacates the middle of the field, the under route will be wide open behind him. Beware of Cover 0 or man blitz packages that show no safety help, the seam route can be a quick strike but you must get the ball out fast before the rush arrives. If the defense shows a robber or lurk defender sitting in the middle of the field reading the quarterback's eyes, avoid staring down the seam route and be ready to work the under route or checkdown quickly.
Check the pre-snap alignment of the slot cornerback or nickel defender before the snap, if he is playing off man with no safety help over the top the seam route is live immediately.
Look at the middle linebacker depth, if he is sitting shallow in a Tampa 2 or Cover 2 shell the under route will have a natural window behind him and in front of the deep safeties.
Use hot routes to convert the flat route into a quick out or speed out against teams that show Cover 0 or man blitz pressure, this gives you a faster outlet than waiting on the seam.
Run this play on early downs like first or second and short to medium yardage since the under route can pick up chunk yardage after the catch if the linebacker bites on the seam fake.
Pair this play with PA WR In or Y Trail in your play-calling sequence, since both look similar out of Box Y Split pre-snap but attack different levels, forcing defenders to hesitate on their run fits and coverage drops.