Playbooks

Curl Flats out of Shotgun Empty Ace spreads five eligible receivers across the formation with no back in the backfield. The backside receiver runs a vertical release into a curl at intermediate depth, the inside receiver on that side sits down in the flat, and the trio to the play side (bunched near the core) run a curl, flat, and a deep vertical clear-out from the number 1 receiver on the far side to stretch the defense horizontally and vertically. This is a classic zone beater built on curl-flat leverage, with the quarterback progression starting at the near-side curl, working down to the flat defender, and checking the backside curl if the coverage rotates away from it.
Pre-snap, check safety depth and alignment, since a single high safety signals Cover 3 or Cover 1, both of which open natural throwing lanes for the curl routes sitting down in the honey hole. Watch the flat defender's initial drop, if he sinks too deep or widens late the flat route will be wide open for an easy checkdown throw. Key the underneath linebacker or nickel defender assigned to the curl zone, if he flies to the flat or bites on the initial vertical stem, the curl will settle in behind him for a big throwing window. This play struggles against aggressive man coverage with a spy or against Cover 4 quarters shells that have safeties sitting on the curl depth, since those alignments take away the intermediate window. Be alert for a user-controlled defender lurking in the shallow zone or jumping the flat route, since aggressive human defenders will often sit on this route combo knowing it is a zone beater staple.
Use pre-snap motion or a hot route check to identify if the defense is playing zone before the snap, since this concept thrives against Cover 2 and Cover 3 shells where the curl sits in the seam between the corner and linebacker.
Attack the flat defender first if the cornerback plays deep and soft, since the flat route will be open underneath against off-man or zone drops.
Pair this play with All Go or Post Wheel Shallow in the same set to keep defenders honest, since both punish defenses that jump the curl-flat combo with linebackers or safeties.
Best called on second or third and medium, where the curl route sitting at the sticks gives the quarterback a high-percentage completion for the first down.
If the defense shows Cover 3 with a hard buzzing safety, hot route the backside curl into a deeper dig or hitch to avoid the flat defender squeezing the window.