Slant–Flat

The concept

One receiver breaking inside, a back running outside underneath him. Two routes, opposite directions, one defender between them.

The offense1 / 3
The look
One receiver breaking hard inside at three yards, and a back running to the flat underneath him. Two routes leaving in opposite directions at the same instant.
vs Man2 / 3
The conflict
Both are covered by whoever is on them. The flat is a hard cover from inside leverage, the slant a hard cover from outside.
vs Man3 / 3
The throw
The flat defender, and nobody else. He picks one and you throw the other. One read, one beat.

Why it works

The simplest horizontal stretch there is
One defender, two routes, opposite ways. Whichever he takes, throw the other one. There is nothing else to understand.
The ball is out before pressure matters
Both routes are available in under two seconds, which makes this the answer to a heavy rush as much as to a coverage.
One read means one mistake to make
There is no progression to work through. Look at the flat defender, throw off him, and be wrong about nothing else.

The slant breaking flat instead of climbing
A slant that runs sideways runs into the linebacker. Three steps and in, still gaining ground — the angle is the route.
The flat route running too deep
Past five yards it is in the same window as the slant, and one defender covers them both. It has to stay underneath.
Staring the defender down
He is reading your eyes as well as the routes. Take the look with your feet already set, not by turning your head to it.

Open it in the designer, change the routes, save it to your playbook.