Monday, July 20, 2009

4-3 and 3-4 Defenses, Part One

by: Matthew Heuett

[Note: I'm getting married on the 25th, so I will be gone from the 21st through the 31st. If I've set things up correctly, parts one through four of this article will be automatically posted each morning.]

One of the more intriguing bits of information to come out of the Seahawks’ recently concluded OTAs was that Aaron Curry was getting plenty of practice in pass rush drills. Speculation about what this could mean for Curry’s role in the defense only intensified when (as Mike Parker reported here) Curry said in an interview with KJR’s Mitch Levy that he “plays linebacker and defensive end.” Given the glut of defensive ends on the roster, many of us began to wonder if this could mean the team was thinking about using Curry not just as a blitzer in the Seahawks’ base 4-3 defense, but also as a pass-rushing outside linebacker in a potential 3-4 alignment package. (Chris Sullivan was kind enough to start the conversation on the possibility of a 3-4 being used in Seattle here.)

But in order to properly evaluate that, we need to understand not just the differences in how personnel are used in the 4-3 and 3-4 defensive schemes, but also what the benefits and drawbacks of each are along with how well Seattle’s roster fits the specific needs of both schemes. Besides, we’re currently stuck in the offseason doldrums anyway, so I figured this was as good a time as any to do another explanatory article (for those who missed it, you can read my previous article explaining the wide receiver positions here).

My original plan was to do all this in one article, but by the time I was done it was so long that I decided to split it up into four installments (I suppose I could have trimmed the length down some, but I’d rather not cheat you guys on information). Today we’ll focus on some defensive scheme history, introduce the 4-3 defense, and take a look at defensive tackles in the 4-3. In part two on Tuesday we’ll examine defensive ends and linebackers in the 4-3. In part three on Wednesday we’ll look at the strengths and weaknesses of the 4-3, introduce the 3-4 defense, and look at how defensive ends and tackles are used in the 3-4. And in part four on Thursday we’ll finish off by looking at linebackers in the 3-4, the strengths and weaknesses of the 3-4 defense, and look at how and why the 4-3 and 3-4 are able to coexist in the modern NFL.

To continue, click

It’s History Lesson Time, Hooray!

I don’t know about you guys, but I have a much easier time grasping concepts when I know how things got to the way they are today, so let’s start with a bit of history so we can see how the 3-4 and 4-3 developed. Back in the early days of football everything was focused on the running game, and for good reason -- forward passes weren’t legal until 1906, and until 1934 the balls used were much rounder, making them harder to throw accurately. As a result, defenses were relatively simple, with nearly every team using the 7-box scheme:

As you can see, the defense used the same personnel as the offense (players went both ways back then). The tackles and ends were the key positions in the 7-box; the ends protected against runs to the outside, and while they did that the tackle had to slide over and stonewall another blocker without letting the offense open up a running lane between him and the guard. The fullback and quarterback worked as linebackers, and the tailback and wingback were used as defensive backs. On those rare occasions when a passing play was called, the quarterback would drop back into deep coverage to work as a safety.

After the shape of the ball changed, the forward pass became a more viable option. As passers like Arnie Herber and Sammy Baugh and receivers like Wayne Millner and Don Hutson began to rack up wins through the air, defenses adapted by switching from the 7-box to a 6-2 alignment:

The only real difference here is that the center now played linebacker instead of defensive lineman, allowing the quarterback to stay in the backfield as a safety. And aside from a few new wrinkles (like double and triple coverage to deal with guys like Hutson and using linebackers to run blitz between the tackles), the 6-2 was run exactly the same way as the 7-box.

The 4-3 Defense

Over the next few decades the passing game continued to gain popularity, so defenses (most notably the Giants in the 1950s under defensive coordinator Tom Landry) adapted once again by replacing two more defensive linemen with a second safety and a brand new type of player, the middle linebacker. And just like that, the 4-3 was born:

With four defensive backs standard now, the coverage schemes and tactics we all know and love (zone, man-to-man, cover-2, quarters, etc.) began to develop over time. However, the assignments and responsibilities of the cornerbacks and safeties in the 4-3 and 3-4 defenses are virtually identical, so we won’t be discussing the DBs much from here on out.

The first major strength of the 4-3 lies in the specialized duties of the defensive linemen -- when all four men do their jobs, they’re more than a match for five offensive linemen (plus a tight end or two from time to time). In order to get a better understanding of what these guys do, here’s a diagram labeling the different gaps and position assignments:

The numbers indicate the basic positions where a d-lineman will typically line up before the snap and are referred to as techniques. The spaces between the offensive linemen (i.e. the lanes through which a running back might carry the ball or a linebacker might blitz to get to the passer) are labeled by letter and are called gaps.

As long as we’re on the subject of terminology here, the right side of the line, which is where the tight end usually lines up, is called the strong side, and the left side of the line is called the weak side. If the tight end were to line up on the other side, those names would be reversed. Whether a player lines up against the strong or weak side of the line also affects the personnel requirements for those positions in the 4-3, as we’ll see when we get to the defensive ends and linebackers.

Defensive Tackles in the 4-3

The first defensive tackle is called the nose guard and usually lines up on the center’s right shoulder in the 1-technique position, although depending on where a play is expected to go, he might shift over to the center’s other shoulder. Since the d-line is outnumbered five to four, it’s the job of the nose guard to even the odds by forcing the center and right guard to double team him, thus leaving the other three defensive linemen in one-on-one matchups. He also clogs up one or both A gaps to deny the offense any opportunity to run there and is close enough to slant over to clog the B gap between the right guard and tackle if the running back tries to get through there.

In order to do the job properly, the nose guard has to be big (as in 6’1”+, 315-350 lbs) as well as strong enough to not only stand his ground against two 300+ lbs linemen but also shove them backwards to collapse the pocket on a regular basis. Last year’s starting nose guard Brandon Mebane (6’1”, 315 lbs) and the probable starter for the ’09 season Colin Cole (6’1”, 330 lbs) are the prototypical size for the position, as is backup nose guard Red Bryant (6’4”, 318 lbs). However, size alone isn’t exactly a hard and fast indicator of whether a player can man the position. Chuck Darby did a fine job as Seattle’s nose guard in ’05 and ’06 despite only measuring 6’0” and weighing 297 lbs, which is closer to the size you’d expect to see in the other DT position. The third player who appears to be practicing at nose guard is Kevin Brown, a 6’2”, 303 lbs practice squad player from last year, but most likely he’ll end up on the practice squad for another season.

The second defensive tackle lines up on the outside shoulder of the left guard in the 3-technique, which is why the DTs that specialize in playing the position are called 3-techs. Simple, is it not? Their job is pretty simple, too: shoot through the B gap and disrupt things in the backfield, whether that means sacking the quarterback on passing downs or taking down the running back for a loss on running downs. The idea is that the center and left tackle will be so busy dealing with the nose guard and right defensive end, respectively, that the 3-tech will constantly face one-on-one matchups against the left guard, increasing the possibility that he’ll be able to break through into the backfield.

Because the position requires much less in the way of standing firm and stonewalling o-linemen, the 3-tech favors a lighter (say, 290-310 lbs), more athletic player with an explosive first step. Departed starter Rocky Bernard (308 lbs) and perennial backup Craig Terrill (295 lbs) both fit the mold in terms of size and speed (well, Bernard did until groin injuries slowed him down last season). Mebane is a touch heavier than the prototypical 3-tech, but his 5.5 sacks last year -- a much more impressive stat when you consider the nose guard position he played doesn’t generally rush the passer -- proves that he has the speed and power necessary to get into the backfield and do some damage.

And that’s it for today. I'd like to give a big thanks to for helping me fill in some details on the 6-2 and 7-Box schemes (info on early football strategy is hard to find, and doubly so for defensive strategies). Tomorrow in part two we’ll look at defensive ends and linebackers in the 4-3.