Continuing with our series of defensive coverage shells, this week we’ll take a closer look at the three-deep zone defense, which is more commonly known as the cover 3.
Green Bay Packers defensive coordinator Dom Capers predominantly prefers the single-high safety look, but he has deployed the cover 2 shell frequently over the years.
However, the Packers don’t use the cover 3 all that often, but it’s a defense that every NFL team must have in their arsenal because what it brings to the table.
Of course, this article comes with my standard disclaimer that this is an oversimplification for illustrative purposes only.
Cover 3 Defense Defined
When defending the field, the defense usually divides the area vertically into “halves.” The underneath half typically extends 7 yards from the line of scrimmage and the deep half usually extends 15-20 from the line of scrimmage.
In the three-deep zone defense (cover 3), the free safety and both cornerbacks play zone defense and each guard a third of the deep half. They must cover any receiver entering their respective third of the field and drive towards to the ball once it is in the air. Additionally, they must carry the receivers vertically all the way to the goal line.
The GIF below highlights the assignments.
Strengths of Cover 3
There is no perfect defense in football. If the defense sells out to stop the run, they are extremely vulnerable to the pass. Likewise, setting up a strong back end to guard the pass makes them susceptible to the pass.
The cover 3 is a compromise defense of sorts. Because the deep third is covered by the free safety and both cornerbacks, the strong safety is free to align in the box.
This means the defense can play eight in the box to stop the run. The front seven (defensive line and linebackers) are in the box in addition to the strong safety.
In a nutshell, the cover 3 allows the defense the flexibility. It can be considered a “jack of all trades” defense. It is a very popular run defense, with pass flex, in the NFL because it allows the defense to pack eight in the box and still drop seven into zone pass coverage.
Weaknesses of Cover 3
The cover 3 is a full zone defense. In contrast, the cover 1 and cover 2 allows the defense flexibility to play man-to-man or zone in the underneath half, including various blitz packages. Also, the cover 1 and cover 2 allow the safeties to provide double coverage over the top.
Since the cover 3 is usually full zone, there is no real opportunity to blitz. Also, since the underneath half is playing zone as well, the deep thirds cannot usually provide double coverage over the top. The underneath defenders must release their receivers once they clear their zone.
Additionally, the cover 3 relies on linebackers to cover any receiver in their zones, who may be quicker and more athletic than they are. As such, the cover 3 is vulnerable to quick and short passes underneath.
Aligning and Playing the Cover 3
When we previously covered the cover 1 and cover 2, we didn’t consider the underneath zones all that much because the cover 1 and cover 2 are basically protective shells over the top of flexible underneath coverages.
However, the cover 3 is typically a full zone, so the deep zones work in tandem with the underneath zones. Each of the zones is assigned to guard specific pass routes, so we must review the route tree below.
In the route tree above, the receiver breaks his routes at different depths. Routes 1 and 2 are part of the three-step game. That means the quarterback take a three-step drops and immediately fires the ball to those routes.
The underneath half is responsible for the three-step game of wide receiver routes, as well as any routes being run from backs from backfield.
Additionally, the underneath zone must be on alert for the 5 and 6 routes (part of the 5 and 7 step game, explained below) because these are defined as comeback routes, where the receiver previously cleared the underneath zone but returns to it while the ball is in the air.
The deep zone is responsible for the 7-9 routes. These are part of the 5 and 7 step game, meaning the quarterback backpedals 5 or 7 steps before throwing the ball.
What defines the 7-9 routes, and the deep zone responsibility, is what is called the “move area.” The move area is the point at which a vertical receiver will break his route in the 5 and 7 step game. The break point varies by offense and play situation, but it generally happens between 10 and 18 yards from the line of scrimmage, making the deep zone responsible for defending the move area.
Now that we understand the basic route assignments, we can look at how the defense aligns before the snap of the ball.
Typically, the free safety shows a singe-high look and the strong safety aligns in the box on run alert. Both cornerbacks play in the box, but may give the wide receivers a generous cushion. They have the difficult assignment of providing run support, but quickly bailing deep into zone coverage on a pass play.
At the snap of the ball, the defense must recognize run or pass. Assuming it’s pass, the defense must rotate into the full zone. Because the linebackers must recognize pass and drop into their zones, they are a weak link in the quick passing game.
The free safety and both cornerbacks must quickly backpedal to achieve depth. The free safety plays between the hashmarks and the cornerbacks play atop the numbers.
The will linebacker is responsible for the weak side flat and the the strong safety is responsible for the strong side flat.
The mike and sam linebackers are responsible for the middle zones.
The GIF below highlights the zone assignments.
For simplicity, we are neglecting the back and tight end routes. However, you can see the major zone assignments.
The will linebacker and strong safety cover the flats and are responsible for the 1-6 routes. The cornerbacks and free safety are responsible for the 7-9 routes.
The cornerbacks and free safety must be conscious of the move area and anticipate the receivers’ breaks and drive to the ball in flight. Since they have no help over the top, the will often play out of phase to apply leverage and have position to drive back to the ball.
The will linebacker and strong safety must carry the receivers through the zone, sometimes in a trail technique. By playing a trail technique, they force the quarterback to elevate the ball over them, which is a more difficult throw. It also allows the cornerbacks the ability to drive downhill towards the ball in the flight.
Also, by playing a trail technique, the will linebacker and strong safety are in position to cover the comeback 5 and 6 routes. They are in front of the receiver and the cornerbacks can drive downhill.
Other times, if the linebackers get enough depth quickly, they can play behind the receivers and carry them through the zone while the play unfolds in front of them. This is desirable for the screen and draw game, as well as short squat routes.
The cover 3 is a good all-around defense because it gives them flexibility in defending the run and pass. It allows them to have eight in the box while providing full zone pass security. It allows the defense to always be facing the ball and having the play unfold in front of them. It doesn’t allow for blitzing or double coverage, so everyone must execute their assignment to avoid getting beat.