What it is

Underneath zones are the areas between the line of scrimmage and the deep zones. The main ones are the flat, the hook-curl area and the middle of the field, which coaches sometimes call the hole.

In a game

The flat is the strip near the sideline, close to the line of scrimmage. The hook-curl area is the space about ten yards deep, where receivers run hooks and curls. The middle is the area in front of the deep safety, where crossing routes and digs end up. Linebackers, nickelbacks and cornerbacks share these areas.

More detail

Underneath defenders have two jobs at once: they must stay close enough to the ball to stop short passes, and deep enough that a receiver cannot slip behind them. Offenses attack the gaps between underneath zones with crossing routes and with quick routes into the flat.

The diagram

1. The flat is next to the sideline, close to the line.
2. The hook-curl zone is about ten yards deep, inside the flat.
3. The middle zone, the hole, sits in front of the deep safety.