Zone defense in American football
Zone coverage schemes require the linebackers and defensive backs to work together to cover certain areas of the field, making it difficult for the opposing quarterback to complete passes.
Zone defenses will generally require linebackers to cover the short and midrange area in the middle of the field, in front of the safeties.
In the following, "cover" refers to the "shell" that the defense rolls into after the snap of the ball, more specifically the number of defenders guarding the deep portion of the field.
The general terminology used to describe this alignment is "Cover #," with "#" being the number of defensive players forming the coverage shell.
[1] Cover 0 is an aggressive scheme that allows for numerous blitz packages, as it is easier for players to drop off their coverage and rush the quarterback.
Examples of these switches include double covering a certain receiver and using defensive help to undercut a route to block a throwing lane.
Cover 1 schemes are usually very aggressive, preferring to proactively disrupt the offense by giving the quarterback little time to make a decision while collapsing the pocket quickly.
This is the main advantage of Cover 1 schemes—the ability to blitz from various pre-snap formations while engaging in complex man-to-man coverage schemes post-snap.
For example, Cover 2 Man means 2 safeties have deep responsibility while the cornerbacks and linebackers follow their offensive assignments in one-on-one coverage.
Teams that play Cover 2 shells usually subscribe to the "bend-but-don't-break" philosophy, preferring to keep offensive players in front of them for short gains while limiting long passes.
This is in stark contrast to the more aggressive Cover 1 type scheme, which leaves the offensive team's wide receivers in single man-to-man coverage with only one deep helper.
In Cover 2, the cornerbacks are considered to be "hard" corners, meaning that they have increased run stopping responsibilities and generally defend against shorter passes.
The "hard" corners also generally bear the responsibility of "pressing" or "jamming" the offensive receivers- disrupting the receivers' intended path downfield.
When the ball is snapped, the safeties will often move toward the sidelines in order to cover any long passes to quick wide receivers.
This disadvantage is ameliorated somewhat in the Tampa 2 variation; however, in moving the middle linebacker into deep coverage, it opens up the "underneath" center zone in the 5-10 yard range.
Another disadvantage of Cover 2 is that it leaves only seven men in the "box" (the area near the ball at the snap) to defend against the run.
A potential problem with Cover 2 is that defensive pressure on the Quarterback must be provided nearly exclusively by the front linemen, as all other defenders are involved in pass coverage.
If the defensive linemen do not provide adequate pressure on the quarterback, the offense is afforded plenty of time to create and exploit passing opportunities.
Its benefit over cover 3 is that it only dedicates two defensive backs to deep coverage rather than three, allowing for better protection against short outside routes.
The Tampa 2 generally requires a quick and agile middle linebacker who is capable of staying with tight ends and wide receivers in pass coverage.
The other safety is free to rotate into the flat area (about 2–4 yards beyond the line of scrimmage), provide pass coverage help, or blitz.
This puts pressure on the outside linebackers to react to pass plays and get into their drop quickly if they need to cover a receiver.
The main weakness of Cover 4 shells is the large amount of space left open by the retreating defensive backs.
On runs, the field side may be spread by a tight end and 2 receiver formation, offering an advantage on the edge.
