What it is

Cover 0 is man-to-man coverage with no safety deep. Every defender covers a receiver, and nobody is left to help over the top.

In a game

Because no safety has to stay back, the defense can send extra pass rushers, often six or even seven. Each remaining defender covers a receiver all over the field. The quarterback must throw before the rush gets to him, and if a receiver beats his defender, there is nobody behind to stop him from scoring.

More detail

Cover 0 is a high-risk call. It is used when the defense wants to overwhelm the pass protection, for example on third down or near the goal line, where there is little space behind the defense anyway. A common version is called Lock. It sends six rushers, the running back is covered by the hook defender, and the other defenders cover #1 and #2 man-to-man.

The diagram

1. There is no safety deep, and every defender covers a receiver.
2. The extra defenders rush the quarterback.
3. If a receiver wins his matchup, nobody can help.