The 4-3 Under defense is the base defensive package that the Seahawks run. Pete Carroll has been running this defense nearly his entire career, so as long as Carroll is the coach of the Seahawks, this is most likely the defense you're going to see on the field.
Carroll started his career out as a graduate assistant at Arkansas under Lou Holtz. At the time, the legendary Monte Kiffin was the defensive coordinator there and had been running a 4-3 defensive variation called the 4-3 Under- (he had run it for a few years prior at Nebraska, had installed it at Arkansas and later ran it while Carroll was with him in Minnesota in the NFL as well). Under Kiffin at Arkansas and Minnesota, Pete Carroll zeroed in on this defensive philosophy and he hasn't wavered from it since. Carroll said: "When I started out coaching I spent three years as a graduate assistant. No one would hire me at first or even send me a rejection letter. A good friend of mine told me that there was a graduate assistant's job open at the University of Arkansas. That was the year Lou Holtz went there as the head coach. I got the position and it was the best thing that ever happened to me.
During that time I got to work with Monte Kiffin's staff on defense. He had been at Nebraska before he came to Arkansas. I think he is one of the best coaches in the United States. He is just an unbelievable coach. He ran a 4-3 under defense that he perfected at Nebraska and they won a national title and many conference titles while he was there in the 1970's. He brought that same defense to Arkansas. I have been running that same base defense since 1977 when I learned it from him. I have used variations of this defense my entire career. I have stayed with its principles through all my years of coaching. I have a real strong belief in this defense. I know the defense and its adjustments so well that my belief system in it is strong and rock solid."
The 4-3 Under, in it's simplest terms, is a gap control system meant to stop the run and to pressure the passer. For the most part, each lineman and linebacker is responsible for one gap - this makes each player's responsibility fairly cut and dry and eliminates a lot of the reads and thinking from the game. Now, the 4-3 Under can be run with 2-gapping personnel as well, and that was something that we saw Red Bryant and Colin Cole doing when they were healthy in 2010, but it really depends on if you have the horses to 2-gap or 1-gap in this system.
As a refresher, here is how the gap and defensive alignment system works.
You see the offensive line on the bottom of that picture as T, G, C, G, T, E. The space between each offensive lineman is a lettered gap. The A gaps are to each side of the center. The B gaps are to the outside shoulder of the guards. The C gaps are to outside shoulder of the tackles. The D gap is on the outside shoulder of a tight end, if he's there.
Similarly, the 'technique' numbering system designates where each defensive lineman lines himself up in relation to the offensive player. As you can see above, an even number 'technique' (0, 2, 4, 6) denotes that a defensive player is lined up helmet to helmet with the opposing offensive player. An odd number denotes that a defensive player is to line up offset from the offensive player. You may hear a lot about the 1-technique, the 3-technique, and the 5-technique in the Seahawks defense. I'll explain each of those as we go along.
In the late 1980's, Monte Kiffin began coaching for the Minnesota Vikings with a coach named Floyd Peters and they further developed the 4-3 Under that emphasized rushing the passer. The 4-3 Under system uses almost exclusively a staggered alignment to the offense in this basic set.
As you can see, in a basic 4-3 Under, the SAM linebacker is lined up to the outside shoulder of the tight end off the line of scrimmage a yard or two and is responsible for the D gap (to the outside of the tight end). He's also responsible for running in pass coverage from time to time. The strongside defensive end is lined up to the outside shoulder of the tackle, in a 5-technique alignment, and is responsible for the C gap (to the right of the tackle). The strongside defensive tackle is usually lined up shading the center in a 1-technique alignment and is responsible for the strongside A gap. The weakside defensive tackle is lined up in a 3-technique alignment off the weakside guard and is responsible for the weakside B gap in front of him. The weakside defensive end is lined up to the outside shoulder of the weakside offensive tackle and is responsible for the C gap on his side.
This leaves the strongside B gap and the weakside A gap open. These are the responsibilities of the MIKE and WILL linebackers.
The 4-3 Under can be run with any combination of secondary assignments, the Cover-1, Cover-2, Cover-3, and even the Cover-4, and the Seahawks run different zone coverages at different times. The number in each "Cover" represents how many players are responsible in zone for the deep part of the field. In a Cover-1, the deep middle safety is responsible as help for the entire deep field, while all the other players are in man coverage. In a Cover-2, there are two safeties and they split the deep part of the field into two zones and help on routes in their zone. Cover three, one safety and two corners have 1/3 of the field as their respective zones. In Cover-4, also known as Quarters, the field is divided into four zones and each of the 4 defensive backs is responsible for his zone. In a Cover-0, each player is on a man and there is no zone help anywhere on the field.
The other coverage you see the Hawks run is called the Tampa-2, which I'll delve into further a little later.
The defense that Pete Carroll now employs uses the basic tenets of the Monte Kiffin 4-3 Under defense and mixes in a variation originally pioneered by the legendary George Seifert in San Francisco. Seifert wanted to create mismatches against the opposing offensive line so he started using his weakside defensive end to rove around and rush the passer from a two-point stance (standing up position). This was the beginning of the "Elephant" position and one that Carroll uses today. We also see this position called the LEO, and in the Hawks' defense can rush standing up or in a three-point stance.
It's the same basic alignment but as you can see, the SAM linebacker comes up closer to the line to play hard contain and the weakside LEO is pushed out a bit, maybe a yard off of the weakside tackle. The LEO's main job is to control the C gap while rushing the passer like a wild banshee and the SAM plays contain against the TE, runs in pass coverage with him, or rushes the passer in some situations.
Here is the basic description of each position in the Pete Carroll 4-3 Under. In a continuing series, I'll get into more specifics about it, but I'll start you out with a general description. The LEO can be a little bit smaller than a normal DE and Pete Carroll tends to like a more athletic and versatile body type for his Elephant position; a guy that can speed rush the QB but also react quick enough to control his gap. Must also be able to drop back into coverage occasionally in zone blitz situations.
The strongside defensive tackle can be short and squat but must be able to take on a double team consistently. The weakside defensive tackle, the 3-tech, must be your premiere interior pass rusher and have an explosive first step. His main job is to pressure the QB and stop the run in his weakside B gap. The 5-tech defensive end can be a bigger guy and must be great against the run. This is why you saw Red Bryant move out there in 2010.
The SAM linebacker needs to be athletic and rangy; great against the run but able to run with tight ends and running backs in pass coverage. The WILL linebacker is going to get a lot of tackles and in Pete's system is typically a faster, smaller linebacker with range. The MIKE linebacker needs to be the field general; very instinctual and savvy. He needs to be quick enough to drop back down the middle third of the field in pass coverage in the Tampa-2 coverage. The free safety is a guy that's going to move around a lot and be very instinctual as well. He's going to come up to the line a lot and will get a lot of tackles. The strong safety has to be good against the run but like the free safety, will move around a lot and have to defend against the deep pass a lot. He will need to be fast and have some ball skills.
Finally, the cornerbacks need to be physical and long. They will get involved in run defense a lot so they must be good tacklers. They are protected over the top a lot of the time so typically they're not all-world defenders but need to be pretty fast. You see Pete running with solid, physical and tall corners but in his tenure at USC we didn't see any all-world prospects come into the NFL.
So that's an introduction. Tip of the cap to Scott Enyeart for his descriptions of Pete Carroll's defense and his philosophy in a podcast with Hawk Blogger; Trojan Football Analysis and Jene Bramel for their write-ups on the subject. Also, big thanks to friends of the blog Davis Hsu and Matt Nichols; we've talked through this thing a lot, came up with what we think is happening and will happen, and hopefully it will give you guys a good picture of what we're running here in Seattle. In my next installment I'll describe in more detail the specific type of 4-3 Under we see the Hawks running then go on to describe each position in further detail as well. What I described above is what he ran at USC but Carroll didn't bring that exact defense to the NFL. Stay tuned...