A term used in football to describe any the defensive alignment and obligations of defensive backs. Exclusive to passing defense, defensive backs are responsible for covering a portion of the field (or “shell”) as a strategy for preventing completions or tackling receivers following a completion.
All coverage shell schemes are referred to as “Cover #,” with the number denoting one or more players with specific defensive assignments for the shell in question. For example, in a “Cover 2” defense, the free safety and strong safety are each responsible for one half of the field and play deep coverage. In this scheme, the cornerbacks are “hard corners,” abandoning deep coverage to help guard against the run or short passes. This allows for more defensive versatility at the line of scrimmage, but can make teams vulnerable to passes to the middle of the field. The other main coverage shell schemes are Cover 0, Cover 1, Cover 3, Cover 4 and Cover 6. Each scheme has its own advantages and disadvantages and generally depending on the down, distance and other strategic factors of a game.