Packers Film Room: Jeff Hafley’s 4-3 defensive fronts

The Green Bay Packers’ move to a 4-3 single high safety defense under Jeff Hafley is a significant departure from the 3-4 2-gap quarters-style scheme they previously played under Joe Barry. This scheme was inspired by Vic Fangio’s defensive schemes, thanks in large part to Barry’s time with Brandon Staley. It was introduced at a time in the NFL when teams were beginning to play more two-deep/quarters defenses to limit the explosive passing plays that the new wave of Shanahan offenses were producing.

Under Hafley, the goal is to play more aggressive man coverage or zone coverage with a high safety defense where defensive backs can “pin their ears” and more aggressively engage the passer (and adjust the run) in a 1-gap defense. The defense will likely be more similar to his time working with Robert Saleh in San Francisco (2017 and 2018) and, more recently, Hafley’s defense at Boston College.

The single-high scheme Halfey will implement has its roots largely in the Pete Carrol system made famous by the Legion of Boom in the early 2010s, although it goes back even further into Carrol’s roots. In 1995, Pete Carroll was the 49ers’ defensive coordinator, adopting elements he learned while coaching under Monte Kiffin before embarking on his current path.

1-gap versus gap and half versus 2-gap

It can be difficult to visually distinguish between a 1-gap and a 2-gap defensive lineman when watching a game, even if it’s a familiar 4-3 or 3-4 front. One way to differentiate is to get some of the many playbooks floating around the internet. You can see some of the origins of this defense in this classic 1992 49ers defensive playbook. A term they often use is “basic 2-way read, controlling strong and weak A-gaps” for the 2-gap technique.

Another way to identify on film what specific gap techniques the defensive line is using is to watch a particular defender’s technique. The key indicator of rush technique is the defender’s hand position. The linked video goes into more detail on how to train this technique.

In the 1-gap rush technique, the defender places his hands on the sternum and outside arm of the offensive lineman in the gap, with the defensive lineman’s head in the same gap. In the 2-gap technique, the defensive lineman attempts to rush toward the blocker with his head up while his hands control the blocker’s armpits, thumbs up, elbows turned in. The defensive lineman looks for the ball, leaving the blocker behind him and filling the gap on either side of his blocker.

Under Mike Pettine, the Packers were primarily a 2-gap 3-4 defense. Under Joe Barry, they were primarily a gap-and-a-half defense. In theory, gap-and-a-half allows the edges of the defense to create an overlap in the first level, allowing second- and third-level defenders to easily match the run. For example, gap assignments in the penny front allow the defense to match the run of two deep safeties, or at least remove a safety from the matchup so he can read and fill in as needed.

This requires the defensive players up front to play an additional half-gap depending on the direction of play. The 3-tech defensive ends in the B-gap play a “gap-and-a-half” by playing the B-gaps and squeezing the outside half of the A-gaps, while the nose tackle 2-gap plays the inside half of both A-gaps.

Carrol’s evolution to the Seattle scheme used a mix of 1-and-2 gap principles that allowed the defensive line to block the run and close their gaps. This is significantly different from the Packers’ usual style of play, in which the linemen up front would slowly play their gap to give the defensive backs time to adjust to the run.

There are elements of the 1-gap/2-gap hybrid, but it is unclear if the Packers will actually incorporate these into the front.

Gaps in the defensive line

4-3 Lower Front

Regardless, they will likely play the 4-3 Even “Under Front” most of the time. Hafley’s Boston College defense played most of their snaps in an Under Front with some reps in an Over Front. The days of playing in an Odd Front are over for now.

• Even Front – even number of players at the line of scrimmage in the penalty box.
• Odd Front – odd number of players at the line of scrimmage in the box.

In an under front, the strong side defensive tackle lines up with the tight end in the 1-technique and the weak side tackle lines up with the weak side in the 3-technique. The 4-3 under defense is an aggressive single gap rush defense that tries to do two things: stop the run or pressure the pass with an aggressive upfield rush.

The 4-3 Under has each defensive lineman and linebacker responsible for a single gap, allowing players to play more instinctively and without thinking, which was a common problem in former defensive coordinator Joe Barry’s defenses over the past three seasons.

In an underfront, depending on the strength of the offensive formation, a defensive end plays the 4 or 5 technique and the nose tackle plays the 1 technique and lines up on the closed side (or strong side with the tight end) of the formation.

Also on the strong side is the “SAM” or “OTTO” linebacker, who lines up over the tight end (OTTO is a common term in the Pete Carrol line). The nose tackle and defensive end are usually the best run stoppers, while the SAM linebacker must be able to hold the ball against the run and drop consistently in coverage.

On the other side of the formation (the weak or open side) are the defense’s two best pass rushers, the 3-technique defensive tackle and the so-called “LEO,” or weak side defensive end. The LEO lines up on the outside shoulder of the weak side offensive tackle, leaving linebackers “MIKE” and “WILL” to cover the gap between the strong “B” and the weak “A” (it’s unclear if Hafley uses these terms in his defense).

4-3 About Front

Another variation we are likely to see is the 4-3 “over” front.

In the “over” front, the 1-tech nose tackle is off the strong side and lines up in the “A” gap on the weak side, with the LEO also on that side. On the strong side, there is a 3-technique tackle and either a 5- or 6-technique defensive end.

Another indication is the depth of the linebackers, with SAM playing in the 2nd level with linebackers MIKE and WILL. This is more of a traditional 4-3 front.

Linebacker run fits

The linebackers’ running fits in a 4-3 are also fairly straightforward, with the linebackers typically fitting into the uncovered gap. There are always adjustments, but generally the linebackers primarily fit into the gap they are lined up over but without the ball, with an outside linebacker on the ball acting as an edge setter in some scenarios.

The linebacker lineups in a 4-3 defense are the same as the defensive line just established in the 10s. An A-gap linebacker is a 10 lineup, a linebacker over the middle is a “00.” Lineups in a 4-3 underfield typically place one linebacker on the ball, usually the SAM linebacker, and linebacker lineups in a 4-3 overfield typically place all three behind the front away from the ball.

In Part 3, we’ll look at the coverages we’re likely to see behind the 4-3 front this year, as well as some subpackage blitzes and pressure situations.