The defensive line is very important. In any defense. Like every other defense, the defensive line in the 4-3 defense is very, very important. Let's talk about how Pete Carroll views each position in his basic 4-3 Under scheme.
The basic philosophy, as Pete Carroll put it, involves the idea that, "The more the attacking oriented the defense is the better off it will be. Obviously when you come off the ball, sometimes it is run and sometimes it is pass. We like to be in the mode of attacking the line of scrimmage, so when it is a pass we will get pressure on the quarterback."
The 4-3 Under is geared to stop the run and get pressure on the quarterback, in it's simplest terms. You want to have attacking defensive linemen that can sniff out the run but if it's a pass, get to the quarterback and force a bad throw or get a sack.
So how does Carroll describe each position? First, the strong-side defensive end, also known as the 5-tech:
"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."
This is the position that Red Bryant occupied for the first seven games of 2010, and a spot that he held down well while two-gapping. After Bryant went down, the Seahawks tried Kentwan Balmer, Jay Richardson, and a few others at the position but none had the effectiveness of Big Red. Eventually, Carroll relented and put Raheem Brock there in a more traditional 4-3 role where he got up and rushed the passer. For the most part, the way that Carroll envisions it, Bryant, or a bigger run stuffing defensive linemen, sits back and takes care of two gaps, primarily concerned about stopping the run. In obvious passing downs though, his goal is to push the pocket and create a vice for the quarterback as best as he can.
The 5-tech player in this defense can be bigger, significantly bigger, than a normal 4-3 defensive end. Red Bryant is 6'4, 323 and most probably the biggest dude at that position in the NFL. But Bryant has a pretty rare combination of speed and size so you're not going to find many players in his mold. The Hawks looked to add some depth at the position by drafting EJ Wilson last season - which didn't work out. They drafted Pep Levingston in the 7th round of this year's draft in their continued search. He is 6'2, 292 and was known for stopping the run in college. We'll see if he can catch on as depth.
Now, the nose tackle, also known as the 1-tech. Colin Cole held down this position for a large part of the season.
Carroll: "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."
Cole did some two-gapping in 2010 as well, which was a departure from Carroll's methodology at USC. For the Hawks, Cole did his best to plug up the middle to take some pressure off the linebacker behind him, typically Lofa Tatupu. Basically, whoever is manning the 1-tech has to be big and squat, and plug up the middle. The Hawks did nothing to bolster that position in the draft but did sign Jay Alford during the early offseason, a guy that could possibly provide depth at the position.
Now, on to the 3-tech. Brandon Mebane was the Seahawks' primary 3-tech when healthy in 2010.
"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."
The key sentence here is "the 3 technique player should be your premiere interior pass rusher." Because the 4-3 is geared to stop the run, it necessitates getting pressure on the quarterback in order to stop the pass. Mebane is a very talented player but failed to get enough pressure on the quarterback in 2010. This could be a reason the Seahawks seem to value him less than most pundits and other 4-3 teams value him. I'm not sure, but because this position is so important, the Seahawks may be looking to find a more disruptive player in free agency or trades to man the position. I wonder if Warren Sapp is available.
In terms of size, I'd say that over 6'2 and around 300 pounds would be the standard for the 3-tech. He must be strong and big enough to hold up against the run but also quick and agile enough to get off his block and get to the quarterback. This is one of the hardest players in the NFL to find. So, good luck to the Seahawks on this one if they let Mebane go.
Finally, the other defensive end, also known as the LEO or Elephant.
"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."
The LEO does not necessarily need to be in a down position. This is one reason many people can be foggy as to whether the Hawks run a 4-3 or a 3-4. With, at times, only 3 men in the 'down' position, it can appear to be a 3-4. In 2010, as I seem to remember it, Chris Clemons ran at the LEO spot mostly from the 3-point, down position. And he did very well there, racking up 11 sacks and playing the run well.
Like Carroll stipulates, Clemons is extremely athletic and proved to be a very good football player. The Hawks have experimented with many players at the position over the last year; Nick Reed, Ricky Foley, and others have come and gone. Clemons was a virtual unknown before the Hawks traded for him but turned out great. The other player the Seahawks have as depth at the position is Dexter Davis, and undersized and athletic OLB/DE out of Arizona State.
In my mind, he's a great candidate to earn more snaps this season and showed a pretty good ability to get to the QB in the preseason last year. If he can effectively hold up against the run, he could surprise some people.
The LEO is another 'tweener' spot that Seattle can benefit from. They have shown an ability to find players that don't fit in other schemes and make them effective. With this ability, look for the Hawks to bring on several 'cast-offs' in camp to play at the LEO spot and try to earn a roster spot.
PC quotes come from two great Trojan Football Analysis articles, so tip of the cap to them, here, and here.