What it is

A hot route is a change that a receiver makes to his route when he sees a blitz, so that the quarterback has a quick target.

In a game

The receiver and the quarterback must read the same thing at the same time. A hot route usually turns into a short route, such as a slant or a quick out.

More detail

A hot route is usually a pre-agreed adjustment, such as a slant or a short comeback against a blitz. The quarterback signals it before the snap, or the receiver reads the blitz and changes the route himself. Sight adjustments rely on practice, so that both players make the same decision.

Animated diagram

1. The slot receiver was supposed to run straight up the field, as the dotted line shows.
2. Before the snap the quarterback and receiver see that a linebacker is about to blitz.
3. The receiver turns his route into a short, quick cut. The quarterback throws it right away, before the blitzer arrives.