The Seahawks defense was up and down, much like the offense, in 2010. It's understandable when switching to a whole new defensive scheme (and it is quite different).
The Seahawks ran a unique defense in today's NFL. To the untrained eye it looks like a 4-3 with a stand-up end, and in a lot of ways it is. However, delve deeper, and it's actually much different than your standard 4-3 defense.
Before I move on, I'd like you take a look at this:
When I say "1 technique" later on, I am referring to the position the player plays. It is marked on this picture as 1. The same goes for 3 tech, 5, 7, etc. The 1 and 3 are never on the same side.
The letters are the corresponding gaps. For example, when you hear announcers say "A-gap Pressure", it means the defense is bringing heat straight up the middle or through the A-gap or gaps.
You can find a better explanation of this here.
Anyway, the 4-3 and 3-4 very often will have strict right defensive end or left rush linebacker positions. Green Bay almost strictly had Clay Mathews line up on the left side of the defense, regardless of strength, in the Super Bowl.
Chicago almost always has Julius Peppers on the right side, most likely so he can attack a quarterback's blind side when pass rushing.
Seattle's defense does not do that. Its strong-side end always lines up on the—you guessed it—strong side. They determine the strong side by strength of the offense.
This is an I-formation. The tight end tips off the strength. For a defense, this is strong left.
What this means for Seattle is that Red Bryant will line up in the 5 tech. on the strong side, or in this case, left side. Brandon Mebane will be beside him in a 3 tech. or "B" gap.
On the weak side 1 tech. will usually be Colin Cole and Chris Clemons the stand-up end. This is why you say all that shifting pre-snap this year.
Side note: This is why you'll see some offenses in the Ace-formation:
In the 2010 season, the Seahawks ran a lot of plays out of Ace (or double tight, single set back, etc). It's used to cause strength confusion. Defenses usually pick the quarterback's throwing side as their strength side. It exposes one side of the defense to stretch plays, making it very popular by zone-blocking teams.
The 4-3 defense has one true run-stuffer, its 1 tech. In past years, Minnesota’s Pat Williams stuffed the run and commanded double teams. His play freed up single-teams for Ray Edwards, Kevin Williams and Jared Allen. Pat was the guy that made that defensive line one of the best.
The 3-4 defense is a little different. Whereas the 4-3 is all about gaps, the 3-4 is more about the linemen controlling their man or men.
The 3-4 nose tackle (the Jay Ratliff, Jamal Williams, Paul Soliai type players) is there to take up space. The 5 techniques in this system are there to occupy their man. Their man is very often a tackle. You never hear of these kinds of players, but they are vital.
The LEO defense is unique. It relies on two immovable objects to get the job done. The 5 and 1 tech need to be able to hold two blockers and be immovable objects that don't necessarily make plays against the run, but free up other players to make them. They cannot be blocked with one man. Against the pass, they'll usually only make plays when the quarterback holds onto the ball too long.
Also the 3 tech. and LEO end have to win their one-on-one matchups. They need to explode through the cracks and make plays in the backfield on runs and passes. If they do that, the zone-type defense will work.
I do not believe this defensive scheme is flawed. It is strikingly similar to the two down lineman defense that Green Bay rode to the Super Bowl.
What Seattle needs to do this offseason is invest in the right parts. The single most important part of this defense is those two immovable objects.
This year, when Red Bryant was healthy, he did his part. He re-established the line of scrimmage and shut down the C and D gap runs to his side. He collapsed the pocket slowly but surely against the pass.
Colin Cole and other 1 and 5 techs did not. They were almost always blocked with one man and pushed back two yards on every play.
They, especially Cole, offered very little pass-rush. This can be attributed to the fact that part of a 1 tech's job is to hunt for screens and draw plays.
We were continually gashed by screens all year.
An upgrade and some depth, preferably through the draft, is needed on the defense. If we do not take a quarterback early on, I vote for Phil Taylor, DT, Baylor.
He is an immediate upgrade over Colin Cole and an eventual successor to the all-important 5-tech, or Red Bryant.
You can find a video of him and others here
Now that you know a little more about the science behind the madness, you can alter your offseason plans (Hint: Take the money you were going to give Nnandi Asomugha and use it to sign Barry Cofield and re-sign Brandon Mebane).