also: sail · Y-sail · three-level stretch
Three receivers to one side at three different depths, so the defenders on that side are outnumbered vertically. Called sail or Y-sail in the Air Raid, where it is core.
Three receivers release to one side of the field at three different depths, typically a deep route, an intermediate out or sail route, and something short into the flat. The quarterback reads them from deep to short and takes whichever level is uncovered.
The mechanism is counting rather than deception. A zone defense usually has two defenders responsible for that area at those depths, and three routes into two defenders means somebody is open by arithmetic. It is the same logic as four verticals applied to one side of the field rather than to the whole of it.
It is frequently paired with a rollout, because moving the quarterback toward the flooded side shortens every throw and takes half the field's worth of defenders out of the play.
sail, Y-sail, three-level stretchsmash, dagger, four verticalsFlood, sail and Y-sail are the same concept under different names, and the corpus records Y-sail as one of the concepts appearing in all three Air Raid sources read. The Wing-T's waggle is a flood concept run off run action, which is a good example of the same idea living in two families that share no vocabulary.
One of the more reachable concepts at youth and lower high school level, because the read is top to bottom on one side and the quarterback never has to look at the other half of the field.