When Pete Carroll was first hired by the Seahawks in 2010, he preached that the team would (eventually) field an aggressive, fast, but most of all unique defense on the field that would surprise a lot of teams. He had tagged many positions on the traditional 4-3 scheme that Jim Mora Jr. used the year before and gave them unique characteristics and names; the weak defensive end was now known as a "LEO"; the strong side linebacker will play more up front, akin to a fifth D-Lineman. If the switches weren't confusing enough, then Carroll definitely raised eyebrows with his first transactions on the team.

Fast forward to three years later, and while Carroll has silenced most of the skeptics (me included) with a team ranked #4 in Defensive DVOA and 1st in Points Allowed last season, most of the successes are still shrouded in mystery and confusion of why this scheme works as it does. We know what he's looking for in terms of players - we already analyzed why K.J. Wright, Bruce Irvin, Bobby Wagner, Richard Sherman and many others were drafted instead of more well-rounded players. We focused on how the defense reacts in terms of certain situations and how they compensate for having unique linebackers and a 323 pound player as their 5-Tech defensive end.

But as to where this scheme come from, why it works, and what makes it so unique and effective, we must start with the basics. And amidst all the different names, players and traits littered within this complex blueprint lies the simplicity of its philosophy.Carroll himself summed it up nicely:

"Our defense is a 4-3 scheme with 3-4 personnel. It's just utilizing the special talents of our guys."

And what, you may be asking, does a 4-3 scheme with 3-4 personnel look like? Let's find out.

The 4-3 and 3-4: The Basic Football Defenses

The 4-3 defense, with four down-defensive-linemen and three linebackers, was first developed in the 1950's under legendary coach Tom Landry, who conceptualized it mainly to stop Jim Brown and the running game. This defense focused on the creation and impact of the middle linebacker (then ahead of its time), who not only managed to stop the interior run lanes but at the same time defend the middle of the field on quick/short passes.

Over time, as NFL offenses continued to evolve with the dual-threat TE, the shotgun and many other schemes of its own, the 4-3 also morphed into different variants that are still commonly used by many teams right now, most notably Monte Kiffin's Tampa-2 and Mike Ditka's 46. For example, Kiffin's insistence on speed and coverage eventually would become the norm for most defenses, as is Ditka's concept of consistent blitzing with linebackers. However, its main identities - defending the middle of the field as well as having a balanced mentality towards the pass and run - remains the focus of one of the league's most popular and recognizable defenses.

Now in the 1960's came along a man named Joel Collier, who, like many other coaches before him, also used the 4-3. However, he had one problem: he didn't have much in the linebackers department to work with. So out of desperation, he asked two of his defensive ends to play at the outside linebacker spot, and sure enough, had enough success to make it stick. Collier would bring this scheme to the Denver Broncos and three Super Bowl appearances, and the term "versatile player" stuck.

The 3-4 wouldn't actually turn into a true "3-4" scheme until the two drastic changes from the 70's and 80's followed, where two teams - the Houston Oilers and the New York Giants - would play a big role in revolutionizing NFL defenses to what we see today. The Oilers, who had an innovative defensive lineman in Elvin Bethea and a innovative defensive line coach in Wade Philips, created the "one-gap" approach that favored quickness over size (at the time, almost all D-Linemen were asked to played head-on instead of attacking a gap), so much so that 4-3 defenses would eventually adopt this as the norm when the inclusion of speed was added. The Giants, under Bill Parcells, drafted a outside linebacker from North Carolina named Lawrence Taylor, who would become the first true (and arguably the greatest) 3-4 OLB in the game. Parcells would also unknowingly align Taylor in a formation that would inspire the 4-3 Under alignment, which is what Carroll commonly refers to as his "main" scheme today.

The 4-3 is known for it's simple but balanced formation, speed and tendency to defend the middle of the field. The 3-4 is branded as a pass-protection scheme with a keen ability to disguise and mix-in coverages and blitzes with its 4th linebacker. How does Pete get the best from both worlds?

One Gap, Two Gaps

One of the most distinct differences between the 4-3 and 3-4 (beside the inclusion of a fourth linebacker) is the ideology behind one gapping and two gapping in the defensive line. With the alignment of the defensive end and tackles in the 4-3, it's very clear as to which gap each player has control and responsibility of in run plays:



via www.itsalloverfatman.com

Now in contrast, the 3-4 is more linebacker-oriented and pass defensive, meaning that linemen must be bigger and more controlling within the trenches. This is where two gapping comes into play, and why 3-4 DL usually line up directly in front of a man versus being in a shade like in the 4-3. With 3-4 players in general, they are bigger in size and are usually asked to take on a man (and both gaps next to them):



via cdn.bleacherreport.net

Enter Pete Carroll. Now one of the biggest reasons why this defense is considered a hybrid is because the defensive line mixes between two gapping with certain players (and 3-4 concepts) with one gapping in the traditional 4-3. As you can see here in the 4-3 Under Front, half of the defensive line is two gapping, and the other half is one gapping (Pictures taken from Eric Stoner's impressive article on BCG):

Creating different responsibilities for different players on the line also allow freedom for the linebackers. In a traditional 4-3 under for example, the 4-tech DE above would be shaded more towards the outsider shoulder of the tackle and insider shoulder of the tight end, with control over the gap between the two players. However, by having Red lineup in front of the tackle instead and play two gaps, this gives the SAM, K.J. Wright, more space and leniency in defending the pass, rather than just being stuck on the line of scrimmage. As Carroll explains himself:

"I run (my 4-3 defense) with one gap principles but can also make it work with some two gap principles. In principle we want to give our players a chance to know exactly what they have to defend. We also want to give them an attitude in which to do that. We want to be an attacking, aggressive football team. We don't want to sit and read the play like you often have to with "two-gap" principles of play. We want to attack into the gap at the snap, get off the ball to play on their side of the field and get after the quarterback." The big problem with any "one-gap" approach however is that it allows a ball carrier to get into the secondary if one guy makes a mistake. No matter how aggressive the defense is there is a great amount of discipline that goes with this defense. You have to be very strict about your positioning and the placement of your players. You have to have the ability to maintain relative spacing between your players.

Creating the Position Archetypes

Having re-written an entire new scheme from scratch, Carroll had to also re-write each position on the front seven's strengths, responsibilities and attributes he was looking for in his players. Below is a compilation of what he wanted in his defensive positions during his time in USC: (Note how the language he uses is an equal mix between what you hear in a 4-3 and what you hear in a 3-4)

On the "One-Technique" Nose Guard: "The nose tackle plays in the A gap to the tight end side of the field in our defense. We have done a number of things with this position based upon the opposition at times. We have put him right in the A gap, we have cocked him on the center at times, and as needed we have even played him in a direct shade technique right over the center at times. The way we play him on base defense is as an inside-foot to outside-foot alignment or a 1 technique on the center to the strong side of the alignment."

"At Nose Tackle you have to find a player who likes to mix it up. We want a big guy in there who likes to get down and dirty. He is going to get doubled a lot on the run and pass and is going to get down blocked a lot. He has to be a tough player. This guy can be a short and stubby type of player."

On the Three-Technique: "The prime spot on the defense to the weak side is the B gap player. He is an inside-foot to outside-foot alignment on the offensive guard to his side. He is a 3 technique player. He has B gap control but he can't get reached or hooked by the defense due to the way we align him. The whole scheme of this defense is predicated upon not getting hooked."

"The 3 technique player should be your premier interior pass rusher. He is going to get a lot of one on one blocks as it is hard to double team him because of where he lines up."

On the "Five-Technique": "The defensive end to the tight end side needs to be a defensive player that can play the run. He does not have to be a big time pass rusher, but he has to play the C gap and stop the run. [He] must works for leverage and force and allow the Free Safety to work off of the him and fills where he is needed on run plays.

On the LEO: "The best pass rusher on the team is usually the defensive end to the open side of the field. That puts him on the quarterback's blind side and makes him a C gap player in this defense. We often align him wider than this in order to give him a better angle of attack and allow him to play in space. We align him a yard outside of the offensive tackle most of the time. He has to play C gap run support but at the same time he is rushing the passer like it is third and ten. He has to be able to close down however if the tackle blocks down on him."

"(He) has to be one of your best football players. Size does not matter as much. We want an athletic player who can move around."

On the SAM: "The Sam linebacker controls the D gap to his side of the field. He is in an inside-foot to outside-foot alignment on the tight end or what most coaches call a 9 technique spot. He can never get reach blocked by the tight end in this position.

"He is the force player for everything run to his side of the field and turns everything back inside to the pursuit. Often he has the tight end in man to man in coverage. He has him anywhere he goes for this defensive call. He never switches if we are in this coverage and will go with him if the tight end does go in motion. He also has to be a good containment player. He has to be big and strong enough to play on the edge of the tight end. He has to be able to run in pass coverage also."

On the MIKE: "The Mike linebacker is in an inside-foot to out-side foot alignment on the offensive guard on his side of the field. He's a traditional middle linebacker. He is instinctive and makes a lot of calls for the defense. He may be the guy with the most experience or the best feel for the game."

On the WILL: "The Will linebacker is aligned against the offensive guard to his side of the field. He is basically a protected player in this alignment and should make a lot of tackles. He has to control his weak-side A gap and play relative to the Mike linebacker and the Free Safety. In coverage, he often plays the short middle.

"The Will linebacker can be a smaller player. He is generally protected in the defensive schemes and will not see as many blocks. All you want him to do most plays is flow and chase the football. We want our fastest linebacker at this position."

Of course, not all of these philosophies really fit in with what the Seahawks are doing right now, and hawk-eyed (HA!) fans will be quick to notice that the Seahawks frequently played Brandon Mebane at 1-technique and Alan Branch at 3-technique when their positions should be switched respectively. Mebane has a unique and impressive skill set with the that warrants another philosophy and purpose in the 1-technique that is perhaps even more successful. Likewise, Branch also frequently rotated in with Jason Jones before he got injured, and I expect that Tony McDaniels, Michael Bennett, Jordan Hill and Jesse Williams will be splitting time there. We'll discuss later on how the idiosyncrasies that the defensive line depth has will create a more dynamic and different concept than what Pete originally stated here.

The Three Main Schemes:

Carroll ended up creating three main fronts that the Seahawks consistently use in their three years: the 4-3 Under, the 4-3 Over, and the "3-4" Bear front. For the 4-3 Under:







This was the main scheme for the Seahawks three years ago when the team was limited in terms of players and a lack of young talent. With slower players at the LB corp in David Hawthorne, Leroy Hill and Lofa Tatupu as well as little depth behind Colin Cole and Brandon Mebane at DT, Carroll was forced to adjust with simpler characteristics that would allow for brief success. Now with a more developed team and different types of players on the roster, I believe the 4-3 under will be more prominent again for a totally different and more effective result.

You can see above the 3-4 influences again within the 4-3 scheme. Brandon Mebane is "two gapping" at the one technique by playing at a slanted angle towards the center (more on that can be read here) and crashing down on both gaps. Red Bryant, in front of the tackle, has the manpower and positioning to deal with both holes around the tight end and tackle. Both of these players can be rotated in with a more pass-oriented, say the team is up by 20+ by rotating in Jordan Hill at Three and Michael Bennett at Five, or a more run-oriented look with Jesse Williams at Three as well. This type of versatility was missed in 2010 and really brought down the level of potential this scheme has with the right players.

(I placed our newest addition, Cliff Avril, at SAM because I believe he will act more as a pass rusher/run defender rather than a coverage man, though i could be wrong. In concordance, both K.J. Wright and Bruce Irvin can play there as well, but that's for another article. )

Not much excitement or difference here, but this perhaps the crux in explaining why this is not simply a "4-3 defense". Now let's look at the more traditional 4-3 over that the Seahawks played more with in 2011:









It's a clear distinction the two gap philosophies still pertain to Carroll's scheme. Remember what I said about the 4-3 being strong in the run? This is where the addition of Red Bryant becomes important, and by having a mismatch on the TE it forces the offensive linemen to either let the TE block Red by itself, or force a double team which frees up the linebackers to make the tackle (which is another basic philosophy of the 4-3 defense - this is why Tampa Bay valued Derrick Brooks so much).

Smith comes in at WILL and Wright returns to his usual SAM spot, which again gives the defense flexibility in protecting the pass and defending the run. Clemons as the LEO also technically move in a little bit from the wide stance away shown in the 4-3 Under to guard against the outside and contain the run. However, by lining up outside the edge Clemons also has a quicker path towards the QB in the pass. Mebane as the interior DT also shifts from a 1-technique to inching a bit closer as the nose tackle, which is evident of the 3-4 philosophy.

Speaking of 3-4, here's the actual front and why a lot of us call this a "hybrid" defense:









As our own Danny Kelly states: "This isn't something you saw every week with a ton of frequency, but it's why Bradley talks about how teams must prepare for the Seahawks as both a 3-4 and a 4-3 - because they have tendencies for both. In essence, the Seahawks are a 4-3 team - it's what Pete Carroll has run for the past couple decades and I really don't know if he's willing to just switch to a pure 3-4. That said, Carroll has shown a willingness to get creative with his players and talent available, and show some exotic looks to confuse and disorient the offense."

Disorienting it is. The two outside ends line up on the line as rushers (and technically counted as DE's) but can drop into coverage. Meanwhile, the plug of McDaniel, Mebane and Bryant stuffs the middle four gaps, leaving Wagner and Smith to defend the middle pass or blitz. Versatility of the 3-4, concepts of the 4-3. This is what Carroll's scheme is all about.

On the next article we'll delve into more history behind Pete Carroll's upbringing and how each aspect of this 4-3 hybrid was derived & evolved from/with his experiences, as well as a further development into why he favors certain qualities in each of his positions over others.