Zone defense in American football
Zone coverage is a gridiron football pass coverage scheme in which defenders are responsible for covering specified areas of the field rather than following individual receivers. In typical zone coverages, linebackers and defensive backs divide the field into underneath and deep zones, attempting to limit passing lanes, keep receivers in front of the defense, and rally to tackle after completions. Zone coverage is commonly contrasted with man-to-man defense, where each defender is assigned an eligible receiver.
Types of zone coverage
Coverage shells
In the following, "cover" refers to the deep coverage structure. Coverage shells can be paired with either zone or man principles underneath; for example, Cover 0 and Cover 1 are typically associated with man coverage, while Cover 2–6 are commonly associated with zone coverages. The number in "Cover #" typically refers to the number of defenders with deep coverage responsibility.Underneath coverage (beneath the shell)
The deep shell describes the defenders responsible for the deep portions of the field. Underneath, a defense may play zone drops or man coverage, depending on the call and situation.Cover 2
In traditional Cover 2 schemes, the free safety and strong safety have deep responsibilities, each guarding half of the field. The primary difference between traditional cover 2 and Tampa-2 is the responsibility of the middle linebacker. In traditional cover 2, the middle linebacker covers the underneath zone, with the two safeties taking responsibility for half of the field in the deep zone. Tampa 2 is a hybrid of cover 2 and cover 3 where the deep safeties have responsibility only for the deep zone "outside the hash marks," while the middle linebacker drops into the middle quarter of the field, covering deep passes between the hash marks.Cover 2 can be run from any seven-man defensive fronts such as the 3-4 defense and the 4-3 defense. Various "underneath" coverages played by cornerbacks and linebackers may also be implemented. 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. Cover 2 can also be paired with underneath zone schemes: Cover 2 Zone refers to 2 safeties with deep responsibility, but now the CBs and LBs drop back into specific coverage zones where they defend passes only in their assigned area.
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. By splitting the deep field between two defenders, the defense can drastically reduce the number of long gains.
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. However, if two receivers run a deep route on a certain side of the field, that side's corner has deep coverage responsibility as well. The "hard" corners also generally bear the responsibility of "pressing" or "jamming" the offensive receivers- disrupting the receivers' intended path downfield. It also relies heavily on the "Mike" linebacker's ability to quickly drop deep downfield into pass coverage when he reads a pass.
A variant of Cover 2 is the Inverted Cover 2, in which either right before or after the snap the corners "bail" out while the safeties come up—in effect switching responsibilities. This strategy may be employed to trick a quarterback who has not correctly interpreted the shift. The main drawback here is that the middle of the field is left open.
Advantages
The advantage of cover 2 is that it provides great versatility to the defense because the corners can play run, short pass, and deep pass with the confidence that they have support from two deep safeties.Disadvantages
The main weakness of the Cover 2 shell occurs in the middle of the field between the safeties. When the ball is hiked, the safeties will often move toward the sidelines in order to cover any long passes to quick wide receivers. This movement creates a natural hole between the safeties that can be attacked. By sending a receiver into the hole, the offense forces the safety to make a decision: play the vulnerable hole or help out on the wide receiver. The quarterback reads the safety's decision and decides on the best matchup. 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. There is also a little pocket on the sideline in between the top of the corner's zone and the bottom of the safety's zone. If the wide receiver were to run up the sideline, there would be a period of time where the corner has to hand the receiver off to the safety. In this window, if a ball is thrown well enough, the receiver is unguarded and able to catch the ball.Routes that work well against Cover 2 are:
corner routes from the inside receiver
skinny post from the inside receiver
post-wheel route concept from the 1 and 2 receiver
4 verticals
Another disadvantage of Cover 2 is that it leaves only seven men in the "box" to defend against the run. In contrast Cover 1 and Cover 3 usually have eight men in the box.
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. Blitzing in Cover 2 often creates greater areas of weakness in the defense than other coverages. Thus, unsuccessful blitzes can prove to be more productive for the offense than in other schemes.
Cover 3
In Cover 3, the two corners and free safety each have responsibility for a deep third of the field, while the strong safety plays like a linebacker. This coverage is generally considered to be a run stopping defense as it focuses on preventing big pass plays and stopping the run while giving up short passes.On the snap, the CBs work for depth, backpedaling into their assigned zone. One safety moves toward the center of the field. The other safety is free to rotate into the flat area, provide pass coverage help, or blitz.
Advantages
One of the biggest benefits of the Cover 3 coverage scheme is the ability to walk the strong safety up into the box with minimal to no changes in the coverage due to the pre-snap center field position of the free safety. This enables the defense to play strong against the run, but still prevent explosive plays such as a long pass or break away run. This advantage is most pronounced versus two tight end sets which naturally creates 8 holes for running backs, whereas in cover 2 schemes there are only 7 defenders in the box leaving 1 hole uncovered, or requiring a defender to cover 2 holes.Disadvantages
Cover 3 schemes are susceptible to short, timed passes to the outside due to the hard drop of both cornerbacks. 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.Another disadvantage of Cover 3 schemes is they are relatively easy to diagnose by opposing quarterbacks. Because of this, teams will often employ slight wrinkles in their coverage to confuse offenses. An example of this includes employing man coverage on one side and zone coverage on another, or swapping coverage zones between defenders. It also leaves the seams open and forces the safety to choose a man to cover on four verticals, leaving one open.
Cover 4
Cover 4, or quarters, refers to 4 deep defenders each guarding one-fourth of the deep zone. Cover 4 schemes are almost always used to defend against deep passes..The most basic Cover 4 scheme involves 3 CBs and 2 safeties. Upon snap, the CBs work for depth, backpedaling into their assigned zone. Both safeties backpedal towards their assigned zone.
As with other coverage shells, Cover 4 is paired with underneath man or zone coverage in its most basic form.
Advantages
The main advantage of a Cover 4 defense is that it is extremely difficult for even the best quarterbacks to complete long passes against it. Therefore, this coverage is generally used as a prevent defense to be used near the end of a game or half, meaning that the defense sacrifices the run and short pass to avoid giving up the big play with the confidence that the clock will soon expire.Cover 4 also has the advantage of using safeties in run support, as opposed to cornerbacks, as would be the case in a Cover 2 scheme. This gives the defense nine in the box and the ability to stop the run with an extra defender on either side. The play-side safety would come up in support on a running play while the back-side safety would be responsible for the middle third of the field, and the cornerbacks would have the deep outside thirds.
Disadvantages
The main weakness of Cover 4 shells is the large amount of space left open by the retreating defensive backs. Since the defensive backs are working for depth, short pass routes underneath can enable the quarterback to make short- and medium- length passes, as well as isolate a defensive back on a wide receiver near the sideline with little help.Cover 6
Cover 6 calls defensive strength to the Field instead of to the offensive formation or front, and organize personnel by field-side player and boundary-side player. The position of the ball on the field therefore dictates the strength of the offense. In Cover 6 the field safety and field corner cover fourths of the field, and depend on a field outside linebacker to support them underneath. The free safety covers the boundary-side deep half, and the boundary corner plays the flat. Thus, the field side of the coverage is quarters, and the boundary side is cover 2.The Cover 6 gets its name from the fact that it combines elements of the Cover 2 and the Cover 4 on the opposite side.
On the strong side, the corner and safety play "Cover 4 rules", which as above the corner and safety each have a quarter of the field working for depth in their zones. The "Sam" linebacker will be dropping outside to cover the flats. If in 3-4 the Middle Backer will cover that sides hook to curl if not blitzing.
On the weak side, the corner and safety play "Cover 2 rules", which as above the corner stays home in the flats, and the safety covers the deep half. The "Will" backer will play hook to curl or blitz depending on the call. If in 3-4 usually the "Will" or the Middle Backer will blitz from that side.
The Cover 6 is also good for calling a corner blitz from the weak side, and having the backer cover flats instead.