What it is

The rat, also called the hole player, is a defender in Cover 1 who has no receiver to cover and instead plays free in the middle of the field underneath, keeping his eyes on the quarterback.

In a game

A hook defender becomes the rat when the running back does not release into a route. He backpedals to a spot about ten yards behind the line, then moves with the quarterback’s eyes to take any pass over the middle. If a receiver runs a shallow route across the field, the defender who loses him yells “Rat!” and the rat picks up the crosser.

More detail

The rat is the reason it is hard to beat man coverage with a deep safety using only crossing routes: a free defender is waiting in the middle. Offenses test him with route combinations that put two receivers across the middle at once, so the rat can only take one of them.

The diagram

1. The rat has no man to cover, so he plays free in the middle.
2. He drops about ten yards and watches the quarterback.
3. When a receiver crosses, he takes him.