In the NFL today, there are two defensive alignments used more than any other: the 3-4 and the 4-3. What are the differences between the two, and how do NFL scouts and general managers find players for each defense?
Background of the 3-4
The 3-4 defense receives its name from the number of down linemen (three) and linebackers (four) used in the alignment. It is widely accepted that coach Chuck Fairbanks helped develop the defense while coaching at the University of Oklahoma. He then brought this new defense to the NFL when he became coach of the New England Patriots in 1973.
It was Fairbanks' vision that has led to 14 teams running a base 3-4 defense in the NFL this season.
The advantage of the 3-4 defense is that with four linebackers on the field you have more speed on the field. The basis is simple—the more athletes, the better.
Background of the 4-3
To understand the 3-4 defense, we have to look at the other defensive alignment popular in the NFL.
Like the 3-4 defense, the 4-3 gets its name from the ratio of defensive linemen to linebackers. A 4-3 defense is seen as the more traditional defensive set of the two, and is used by the majority of NFL teams in 2011.
The 4-3 defense remains popular due to the fact that two defensive tackles is seen as better to stop the run. The bigger the bodies along the defensive line, the better.
The Anatomy of the 3-4
Let’s take a look at the basic layout of the 3-4 defense.
Here we see a standard NFL offense against a 3-4 set. Notice the number of defensive linemen, labeled right end (RE), nose tackle (NT) and left end (LE). The arrows next to these players illustrate which gap in the offensive line they are responsible for covering.
You will hear people refer to the 3-4 defense as a “two-gap system;” this is why.
The black numbers surrounding the offensive linemen above are a numbering system that universally labels the alignment of a player. In a 3-4 defense, the ends are generally in a “five technique” position. As you can see above, this means they are directly in front of, or “head up” on the offensive tackle. The nose tackle is in zero technique, as he’s head up on the center.
The red letters you see here are called “gaps.” This is used more so by the offense to label which hole the running back will come through, but the defense also uses gaps to assign blitzes.
A favorite blitz in the NFL right now is an “A gap” blitz, where the middle linebacker runs through the “A” gap once the ball is snapped.
You will also see four linebackers behind the defensive line. They are, from left to right: strongside linebacker (SLB), middle linebacker (MIKE), middle linebacker (TED) and weakside linebacker (WLB). It is also common to see the strongside linebacker labeled SAM and weakside WILL. In other sets the WILL linebacker is actually aligned where the TED ‘backer is here, with a JACK ‘backer outside. It is common to see the outside linebackers move up toward the line of scrimmage into a “nine” position.
What do these players do, though? For the 3-4 defense to work, every player must keep his assignment. Since this is a two-gap system, if one player along the defensive line fails to do his job, the entire defense will break down.
Job: Lined up in a five-technique, the defensive end has inside-out responsibilities. This means the defensive end must watch the B and C gaps once the ball is snapped. His job is to read the offensive line and the backfield to see where the ball is going.
It’s common for defensive coordinators to assign one gap when slanting the defense to the right or left. Unlike the 4-3 defense, ends in a 3-4 defense are not rushing the quarterback as their first duty. An end in a 3-4 defense is taught to play run-to-pass, meaning his first job is stopping the run.
A defensive end cannot lose containment by taking himself out of the play to rush the quarterback.
Scouting points: A defensive end in a 3-4 defense is generally a player who has experience at defensive tackle while at college. Ideally, the player would be close to 300 lbs and standing at least 6’3” tall. The player must be bigger than a defensive end in a 4-3 defense because of his alignment and his two-gap responsibility. A smaller player would be engulfed by the offensive tackle.
Also, at this position, stopping the run is key. For that job, size is needed.
Ideal size: 6'6", 305 lbs
Job: The nose tackle has one job—plug the middle. A good nose tackle will require a double-team, which by itself closes down the A gap to either side. When a nose tackle draws a double team it also frees at least one of the middle linebackers, as the guard is crashing down on the center instead of trying to block a linebacker.
Scouting points: Nose tackles have no height requirements; they just have to be big. A low center of gravity and exceptional strength are key for the position. As a general rule, the bigger the better.
The nose tackle must be able to command a double-team. A big player cannot work in this system if he is not strong enough to draw and hold the double-team.
Ideal size: 6'2"-6'4", 350 lbs
Outside (SAM/WILL) Linebacker
Job: Each defense varies slightly, but the primary job of an outside linebacker in the 3-4 defense is to rush the quarterback. Ideally, an outside linebacker would be a former defensive end with top-tier athleticism.
Outside linebackers must also be strong enough to make sure that no one gets outside him (from the center to the sideline) in the run game—this is called “setting the edge” and is one of the most important factors for an outside linebacker working against the run.
Scouting points: College scouts look for smaller defensive ends with high-level speed and flexibility to make the move to outside linebacker in a 3-4 defense. The best outside linebackers for this defense are undersized ends who can make the move to playing in space.
Since few teams ask their outside linebackers to drop into pass coverage, this is not something that scouts spend much time evaluating. The key is speed, flexible hips and strong hands to beat blockers.
Ideal size: 6'3", 235 lbs, 4.6 (or under) 40-yard dash
Inside (MIKE/TED) Linebacker
Job: The job of a MIKE or TED linebacker varies greatly from team to team, but the rules are the same. Your MIKE linebacker is the tackler. He’s the leader of the defense and the guy you want free to run down the football. The TED linebacker, on the other hand, does more to take on blocks and free up the MIKE linebacker to make plays. A TED linebacker will usually be a bit larger and not as fast.
Scouting points: Inside linebackers in a 3-4 defense are very similar to middle linebackers in a 4-3 defense, only bigger. Classically, a smaller player can be fine in a four-man front because he has two defensive tackles protecting him. In a 3-4 defense there is no one between the guard and the linebacker.
Because of this, scouts look for bigger players who are stronger and more capable at fighting through traffic to the ball.
Ideal size: 6'3", 240 lbs, 30 reps of 225 lbs on bench press.
Job: The job of the cornerbacks and safeties does not change in a 3-4 defense. Each team runs their own variations of coverages and has their own requirements for scouting. Coverage is generally universal between the 3-4 and 4-3, with a few exceptions.
The Bottom Line
Some would tell you the 3-4 defense is a fad, or a weaker system, but statistics argue otherwise. During the 2009 season, four of the top-five defenses in the NFL ran a 3-4 defense. In 2010 that number was again four of the top five, and six of the top 10.
The 3-4 has clear advantages. There are more athletes on the field, and with the popularity of the spread offense in the NFL currently, teams are tasked with getting as many speedy defenders on the field as possible.
You can also be more versatile in a 3-4 defense, as the offense never knows if the two outside linebackers will blitz, drop into coverage or mix the two. With a 4-3 defense you can regularly know the front four are coming after your quarterback.
And that's what makes the 3-4 work so well. It's fast and fluid.