The "Red Zone": The red zone is the last 20 yards before the goal lines at both ends of an American football field. Since the field is 100 yards long, the red zone accounts for 40 percent of the football field. By the time a team reaches the red zone, the offense has almost made it to the goal line. The red zone is never marked on the field itself--nothing formally differentiates the red zone from any other part of the field--but becomes an extremely useful tool when planning strategy. Commentators will often speak of the red zone when gauging a team's overall effectiveness. Similarly, coaches often emphasize red zone plays as a means of successfully completing a drive (or stymieing the opponents'). – eHow.com