Defensive football coaches are always looking to devise plans to slow down offenses, and it could be said that the best ones adapt to their opponents on a week-to-week basis, which means they have a different scheme every week.
There isn't one specific defensive scheme that is most effective because offenses are quick to find a way to attack it with success (and there's always a way).
Consequently, we've seen NFL defenses become much more multiple, which means they are integrating several defensive concepts into packages specified to offenses' tendencies.
There are a number of defensive concepts that coaches effectively utilize, such as the 3-4 and 4-3 front, nickel and dime packages and various coverage concepts, such as Man-Free and Quarters. All of these concepts are listed on play sheets because they are the most effective against specific formations and offensive tendencies.
Evidenced by more than two dozen teams that play it, the 3-4 front is arguably the league's most popular front.
It boasts three hefty defensive linemen who can play a variety of techniques while featuring four powerful and quick linebackers who have a variety of assignments, most notably getting downhill and disrupting the offensive backfield.
There's more than a handful of advantages to being able to play the 3-4 front, but the two that stand out the most are run defense and multiple looks.
Run defense is still a significant and crucial aspect of defense today despite the league passing it much more. If a defense is unable to stop the run, the entire playbook opens up for the offense because the defense has not made the offense one-dimensional, which is the goal.
The 3-4 front is effective against the zone concepts teams are running out of backfields today. These concepts include inside and outside zone, which are run laterally to stretch the defense wide, and then abruptly attack downhill. The best way to attack these types of runs is with penetration, and that's what the 3-4 defense offers.
Instead of going laterally, the nose tackle—who is the anchor of the defense—needs to be able to get downhill and knife into the backfield to cut off any possible cutback lanes for the ball-carrier. Once he's done this, the ball-carrier's options are limited; the defense continues to flatten him out and wide to the sideline, ultimately concluding in a tackle for a short gain or loss.
Moreover, the multiple looks that defenses can present to offenses can be very difficult to break down.
Will it be a three- or five-man rush? Which player is dropping in coverage? What are the blocking assignments then?
The issue is that it could be a nose tackle dropping in coverage or a weak-side linebacker on a designed Fire Zone blitz, which is made up of any five rushers and any six players in coverage. It is unpredictable, forcing quarterbacks to break down everything after the snap.
The 3-4 is well known for its unpredictability after the snap, but in recent years, the 4-3 front has become similar.
Defensive coaches who are running defenses with four defensive linemen and three linebackers have become difficult to figure out because they don't just sit back and rush four; they look to do damage with blitzes, such as the aforementioned Fire Zone blitz and safety blitzes.
In the 4-3 Fire Zone blitz, a defensive end typically drops in coverage unexpectedly, as opposed to a linebacker in the 3-4. There also is still the option of a nose tackle or defensive tackle dropping in coverage in both fronts.
The Chicago Bears are an example of this type of front, mixing in both simplified assignments by rushing just four or, at other times, making it confusing for quarterbacks with Brian Urlacher hovering over the line of scrimmage while a safety looks to blitz from afar.
Further, the 4-3 front is one that is different and sometimes preferred to the 3-4 because of its personnel. The 3-4 often has a rotation of players along the defensive line as well as the linebacker positions, while the 4-3 does not.
In the latter, there are possible rotations, but they are not absolutely necessary in order to deal with a specific offensive package. In some cases, the defensive linemen can just stay on the field while the linebackers drop in coverage.
This flexibility is what makes the 4-3 defense appealing to many.
Nickel and Dime
Whether defenses play a 3-4 front or a 4-3, they're probably playing some form of a nickel or dime package behind it.
Nickel and dime packages have taken over the defensive side of the game because they offer endless possibilities and can match with offenses' multiple-receiver sets.
The nickel, which features five defensive backs, and dime, which has six defensive backs, also offer the flexibility of blitz paths. What this means is that there are more directions in which defensive coaches can send their rush defenders when blitzing.
An example of this is the New York Jets, who spend the majority of their defensive snaps in one of the two packages and like to blitz their defensive backs.
They are able to do this better in their nickel and dime packages than they would with their standard front because players such as inside linebacker Bart Scott are not fleet of foot.
This means they are limited in the paths they can take when blitzing. It's unlikely that Scott would get to the quarterback quicker than a defensive back if he went looping around a stunt in front of him.
However, where the Jets and other teams that heavily rely on these packages have run into issues is against the run. Teams like the New England Patriots have sped up the pace of their offense, consequently forcing the defense to stay in their packages, and they effectively ran the ball against them.
Because of this, the packages have evolved to replacing the additional cornerback(s) with a safety or safeties. The New York Giants illustrated this last season and had a lot of success with it, featuring three safeties who could play the run, cover and still offer various blitz paths.
Last but not least, the various coverage concepts that teams utilize on Sundays have become important because there's a plethora of them.
One of the NFL's most popular coverage concepts is one that I've written about multiple times in the past: Quarters.
Quarters coverage has served as the framework and transition to many coverages for defenses because it offers two deep safeties whose priority is run defense. They are responsible for reading the No. 2 potential pass-catcher on the field, which can be a slot receiver or tight end, and determining their assignment based off that.
If the pass-catcher blocks, the safeties come down and play the run. However, if he comes off the line of scrimmage and runs a route, then they are summoned to cover him in most cases.
There are defenses that have built-in rules for the latter situation, such as the safety picking up the tight end after a specific distance is covered. In Quarters, the cornerback traditionally has a pure, man-coverage assignment on the widest receiver, who is labeled No. 1. From there, the linebackers play zone coverage underneath, covering the flats and seam.
There are many variations of Quarters coverage, such as pattern reading, but what makes it so popular is that with one call before the snap, the defensive backfield can rotate and become a completely different coverage.
For example, a call is made by a safety to change the coverage to Man-Free. Man-Free coverage features a safety rotating down into the box, which is easily done from a coverage like Quarters that starts off with two deep safeties.
Subsequently, the free safety plays zone in the middle of the field. The only other change that is made is that it becomes man coverage when the linebackers and strong safety (who is now in the box) become man defenders.
Man-Free, when executed properly, is one of the best coverages in the league, along with Quarters. The reason is it accounts for all potential deep threats while also having enough defenders in the box to handle the opposition's running game.
As one can see, there's not one way to play defense.
If a defensive coordinator tries to win games by relying on a single front or coverage, he's likely to fail miserably because offensive coordinators adjust in-game to what they see and can pick the coverage apart.
Each front, package and coverage has a weakness, which has forced play-callers to rely on multiplicity to assemble an effective defense. This multiplicity comes from an integration of several packages such as the 3-4 and 4-3 fronts, nickel and dime packages and various coverage concepts.
Defenses will have to continue evolving to stay one step ahead of offenses and provide exotic looks that make them reconsider their responsibilities and assignments prior to the snap.