Sail
Three-level vertical stretch to one side
The outside receiver runs a go/fade, the inside slot or TE runs a corner ("sail") route at 12-15 yards, and the flat receiver runs a quick out or swing. This is an elite Cover 3 beater — the CB carries the go route deep, leaving the curl/flat defender alone against the 15-yard corner and the flat route. He cannot cover both because the corner route is too deep. A core Air Raid play (Mumme and Leach's "Y-Sail"). Sean McVay's Rams and the Chiefs feature it extensively.
Route Assignments
Go/fade route to clear the deep CB and create the vertical stretch.
Corner/sail route at 12-15 yards — the primary read against Cover 3.
Flat/swing route — the low read in the three-level stretch.
Backside post — clears the safety. Modern adjustment: converts go to post when defenses jump the sail.
Check-down safety valve to the backside.
Read Progression
Read the curl/flat defender on the trips side. If he sinks to the corner, throw the flat. If he drives on the flat, hit the corner behind him into the void. The go route removes the deep CB from the equation.
Why It Works
The go route removes the deep CB, leaving the curl/flat defender alone against receivers at two different depths (15-yard corner and 3-yard flat). He cannot cover both — the QB throws opposite his movement.