Many years ago, NFL Sundays consisted of power running offenses that featured two main personnel groupings: ‘Pro’ and ‘Ace’. Pro personnel packages consisted of two backs and a single tight end (21), while Ace had the opposite, a single back and two tight ends (12). Because of this offensive philosophy, defensive coordinators often played with an eighth man in the box to stop the running game, leaving a single safety in the middle of the field while the cornerbacks were assigned to wide receivers. While it was predominantly man coverage in those days, with a lot of Cover 1, teams would mix in zone, such as Cover 3, out of their single deep safety alignment.
Cover 3 is a pure zone coverage that has four underneath and three deep defenders. The underneath defenders are often three linebackers and a safety or cornerback, and they’re responsible for splitting up into two separate categories:
Hook – Hook defenders drop to the hashmarks of the field, hoping to fend off any pass receiving threats in the seam.
Curl/Flat - Curl/Flat defenders are responsible for defending outside the hashmarks as well as expanding outside to the flat if there are any threats posed in the area.
Along with the underneath defenders, there are three deep defenders who are mainly defensive backs. In the deep levels of the field, the coverage is divided into thirds by those three defenders, making each of them responsible for 1/3 of the field.
Cover 3 Sky
If there was a variation of Cover 3 that one could call a ‘base’ coverage, it would be Sky.
This coverage is the most popular form of Cover 3 in the NFL. It entails four underneath defenders dividing their coverage into fourths through the use of the aforementioned Hook and Curl/Flat responsibilities while the three deep defenders–the two cornerbacks and single deep safety–split the field into thirds. What gives it the name ‘Sky’ is the strong safety dropping down into the box and serving as not only an underneath pass defender, but as a force defender.
An example of this coverage variation was seen this past Sunday in the Green Bay Packers-Detroit Lions matchup. The Packers, who lined up in their two-man ‘Psycho’ front, have nickel personnel against the Lions’ 11 (1 back, 1 tight end) Gun personnel. Prior to the snap of the ball, Green Bay showed very few signs of Cover 3 Sky, as they aligned in a two-high safety shell while the cornerbacks had their eyes on the quarterback in a loose alignment inside of the receiver, implying a zone coverage such as Cover 2.
However, at the snap of the ball, the Packer revealed their true intentions when the strong safety rolled down to his Curl/Flat responsibility, and the free safety aimed for the middle of the field. The cornerbacks shuffled to their deep third alignment, and the remaining three underneath defenders got to their designated landmarks.
Ultimately, the strong safety–who is the Force defender on this play–ended up having to expand to the flats as the Detroit tight end ran an out route.
Cover 3 Cloud
Another variation of Cover 3 is Cloud.
Cloud coverage has the same principles as Sky, but there’s a slight tweak in the fourth underneath defender. Instead of a strong safety being the Force defender, it’s a cornerback. This makes him the Flat defender, while two safeties and the opposite cornerback drop into deep third responsibilities. The goal of the safety in the flats is to rotate to replace the vacant area.
The two Hook defenders underneath also undergo a slight change in their responsibilities, as they now expand from the Hook to Curl area if there’s a receiving threat present.
Cover 3 Buzz
The last and final variation is known as ‘Buzz’, which stands for linebacker (Backer) force. This coverage makes the rotating strong safety the Hook defender, while the strong side linebacker (SAM) becomes a Curl/Flat defender, and the three deep defenders remain two cornerbacks and a single (free) safety. Below is a video of this coverage from the Football Film Channel.
Although Cover 3 has had its issues with the vertical passing game, it’s still a popular coverage that effectively offers multiple variations. These coverages enable the defense to get an extra defender in the box while being able to choose who the Force defender is, which is a key component of run defense.
Moreover, against the pass, the defensive coordinator can hide the weaknesses of his defenders by allowing them to attack downhill aggressively. Because of this flexibility and simplicity, the Cover 3 remains a staple of defensive playbooks around the NFL.