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Summer of Spags: the front seven in Steve Spagnuolo’s 4-3 scheme

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As the series continues, let’s examine the front seven in the base defense

NFL: New York Giants-Rookie Minicamp William Hauser-USA TODAY Sports

For the past six years, the Kansas City Chiefs defense has been rather stagnant — not only on the field, but also in the coaching staff. Most of the defensive staff came from the same coaching tree and utilized the same attitude and teaching points.

Fortunately, that is no longer the case. The entire staff has been turned over. I, for one, couldn’t be more excited — both because of the potential for improvement and the fun that comes with studying new coaches, schemes and defensive philosophies.

That’s what we’re doing in this second installment of the Summer of Spags series.

Craig Stout is the mastermind behind this series. He’s been gracious enough to let me help. Be sure to read his introduction to the series.

Craig will focus on the secondary while I will cover the defensive linemen and linebackers. Each installment will build on the last. As with any football team breakdown, there will be some crossover in the breakdowns of the front and the secondary; Craig will be covering that.

Prefer to listen rather than read? Craig and I did a broad breakdown on what to expect in this week’s AP Laboratory podcast.

Let’s dive in!


The base defense

While the term base defense is still used in modern football, it actually defines a sub-package — that is, a specific personnel grouping; it’s not unusual for the base sub-package to be used less often than any other.

In the defensive front, base defense refers to a personnel grouping consisting of four defensive linemen and three linebackers; that’s why it’s called a 4-3. For the linemen, it’s a single-gap system; pre-snap responsibilities for each defensive lineman consist of a single gap in the offensive line. The goal is to create penetration along the defensive line — allowing the linebackers to fill the empty holes that remain.

Use: Spagnuolo tends to use the base defense in early-down or short-yardage situations — and most often against 12 (one running back and two tight ends) or 21+ (two running backs and at least one tight end) offensive personnel groupings. So the base defense is primarily used when the offense is more likely to run the ball — or at least when the reward of running outweighs that of passing.

Personnel: Along the defensive line are two defensive ends who tend to be bigger, stronger players; then there is a nose tackle and an Under tackle. The Under tackle is a 3-technique player — that is, one who lines up on the offensive guard’s outside shoulder. During games, the defensive linemen are rotated in and out, so players get rest and fresh legs are always available.

There are three linebackers: a SAM (strong side), a MIKE (middle) and a WILL (weak side). In the base defense, linebackers generally remain in place — although occasionally the WILL will be switched out for a nickel linebacker who is traditionally a better coverage player.

Since Spagnuolo’s base defense is used almost exclusively against running personnel and on non-passing downs, the MIKE tends to be a bigger, stouter, run-defending linebacker who plays in the defensive interior; at Spagnuolo’s last stop, the MIKE wasn’t a three-down player.

As the series continues, there will be more depth on which traits and skills will be needed in all these positions.

Alignment: In Spagnuolo’s base 4-3 scheme, there are three primary alignments. The first is the 4-3 Under.

In this alignment, the Under tackle (outlined in white) lines up on the weak side of the offense — the side with the fewest potential blockers. This puts the nose tackle on the strong side of the formation — often just off the center’s shoulder. The linebackers, however, shift to the strong side. As we see here, usually the SAM is pushed up to the line of scrimmage on the tight end’s outside shoulder.

The second main alignment is the 4-3 Over.

As we see here, this is essentially the same as the 4-3 Under, except the formation is flipped on the defensive line. The Under tackle is lined up on the strong side of the offense and the nose tackle is lined up on the weak side. The linebackers are still shifted to the strong side, with the SAM moved to the LoS (line of scrimmage) over the tight end’s shoulder.

The third alignment is the 4-3 Stack.

This is a more traditional alignment where the linebackers are playing off the LoS. In this example, the defensive line is in an Over shift, but the linebackers are more balanced. For this particular play, the fullback in the backfield is an extra blocker that can quickly cross the formation, which forces the defense to be out-manned to the back side of the play, or move the linebackers closer to the midline of the formation.

In all of these iterations of the base defense, the defensive ends can play anywhere from a 4-technique (inside shoulder of the offensive tackle) to a wide 9-technique (outside shoulder of a second tight end). We’ll get into more detail about this later, but the choice is based partly on formation and partly on a player’s personal preference. The MIKE and WILL also have flexibility in their exact alignment based on the formation of the offense and the general areas they play on a snap-by-snap basis.

The base defense in action

While specific player techniques, assignments and tactics will be discussed later, let’s look at some examples of how the base defense is deployed.

Here, Spagnuolo’s New York Giants defense is initially aligned in a 4-3 Over to their right, which matches the strength of the offense in 12 personnel. As the two tight ends shift across the formation, the SAM follows and the two defensive tackles switch alignments — keeping the same 4-3 Over, but now to their left side.

One quick thing to note: the defensive tackles didn’t switch with each other; they just shifted their alignments. So while there is a preferred nose tackle and a preferred 3-technique Under tackle, they have to be able to play both positions.

On the back end, the safeties also switch roles and alignments, which allows the strong safety to play in the box.

As the run unfolds, the front side of the defense has the bodies in the right places to not only hold contain, but also force the run to stall or go back inside.

The problem with the 4-3 Over is that backside pursuit is minimal — meaning the defensive end or WILL has to beat a block and hold the backside contain. On this play — and this is a relatively frequent occurrence — the strong safety (as the Apex defender) helps regain the numbers advantage, which allows him to crash freely.

The sister coverage of the 4-3 Over is the 4-3 Under shown here.

The defensive line is shifted to the weak side of the offense — the defense’s left — while the linebackers are shifted right (to the strong side) and down on the edge. In terms of numbers, the offense has a balanced formation — but since the ball is on the left hash mark, the right side is considered the strong side. Here we don’t have a safety in the box, which forces the front seven to stop the run against seven blockers.

The Under front is designed around spacing and penetration, setting players into the gaps that best allow them to shoot into the backfield. Even with the line shifted to the back side of the running play, both defensive tackles are able to interrupt the running back’s path as the offensive line tries to work into their blocks. As multiple offensive linemen are forced to address the defensive linemen pressing into gaps, linebackers can press the LoS and get free runs through unoccupied gaps.

The 4-3 Under isn’t without its own faults. As we see here, the play-side defensive end has to not only hold the offensive tackle but also maintain control over the B-gap without giving up ground. The closest defensive lineman to the strong side defensive end is the nose tackle — two gaps away — which forces him to play an interior gap through the offensive tackle.

Here we see a 4-3 Stack alignment with all three linebackers off the LoS. The Giants start out in a 4-3 Under, but after seeing the offense’s formation, they shift into the 4-3 Stack. The defensive line doesn’t shift with the motion but are now in an Over shift.

With the Over shift, the bodies are available to hold up the strong side of the play, so it’s up to the three linebackers to penetrate through backside gaps while holding contain to bring down the ball carrier. Unfortunately for the Giants, you see the MIKE slip under a block and then fall for the running back’s head fake to come out of his run fit — which leads to a modest gain.

So when is each version of the 4-3 front utilized? The answer is both simple and complex.

A large portion of the decision seems to be based upon the opponent — which is a great thing. A 4-3 Under front may find more success against teams that try to run wide zone to the back side, while a 4-3 Over is stouter against power teams.

With that said, here are the rules that seem to be followed most of the time:

  • Over shift if the offense has plus two blockers to the strong side, or has a single plus blocker to the wide side of the field.
  • Under shift if the offense is balanced, or has a single plus blocker to the short (boundary) side of the field.
  • Stack if it’s 21 personnel and a fullback can quickly cross the formation to the back side.

The base defense against the pass

While the base defense will be used against the run as much as possible, there will be snaps where the defense does have to play the pass.

The 4-3 Under provides the best alignment for a pass rush from the base defense since both a defensive end and the Under tackle are set in gaps that ensure one-on-one matchups.

Beyond that, the linebackers are in good positions to defend the hot areas of the field; the SAM is playing up on the LoS outside of the tight end — allowing him to quickly flow into the curl/flat zone — while both the WILL and MIKE are in the middle of the field.

And given that the formation’s use is against heavier personnel, at least one safety can often sink into a shallow or intermediate zone, too. Having three linebackers on the field usually means less square footage can be covered, but given the alignment of these players, they have short drops into their coverage responsibilities.

Finally... it’s important to remember that while the base defense will only be used for about 20% of the defensive snaps, it is the base upon which the sub-packages we’ll discuss in later articles (nickel, dime, etc.) are built.

Moving forward

Now we’ve set the table for the more detailed breakdowns that are coming. This first installment has focused on the team’s alignments and techniques, but moving forward, the breakdowns will focus more on individual skills as we attempt to place Chiefs players into specific positions.

The next time, we’ll break down the front seven in the nickel defense.