Dec 21, 2014; New Orleans, LA, USA; New Orleans Saints quarterback(9) is sacked by Atlanta Falcons defensive tackles(91) and(99) during the third quarter at Mercedes-Benz Superdome. Mandatory Credit: Chuck Cook-USA TODAY Sports

With the draft quickly approaching, eager Atlanta Falcons fans and analysts everywhere will soon learn who will be joining the team as a part of the 2015 draft class.

Until that time, we are somewhat limited in our ability to predict who the Falcons will be starting on defense and what scheme they plan to run.

However, based on some of Dan Quinn’s previous comments and past tendencies, we can begin to assume that Quinn will put into place a variant of the “4-3 under” scheme he utilized and perfected in Seattle.

But what is the 4-3 under? What does it look like? What makes it different than a regular 4-3 defense, and is it really as similar to the 3-4 as some have claimed?

In this article, I’m going to give you an introduction to some of the basic tenets of the 4-3 under. I’ll also be doing a quick comparison to both the regular 4-3 and 3-4 schemes to illustrate some similarities and differences.

A big thanks goes out to Danny Kelly of the SB Nation blog Field Gulls, who has done some fantastic work covering Pete Carroll and Quinn’s schemes. If you want to know more about the 4-3 under, he has a full multi-part series that goes into great detail.

It’s unlikely Quinn will run the exact same system he ran in Seattle, but there’s a lot of good information there regardless.

At it’s heart, the 4-3 under is a “gap control scheme”. It’s first focus is stopping the run, but it has been adapted over the years to become equally adept at rushing the passer. But what is a “gap control scheme” you might ask?

Essentially, a gap control scheme assigns one “gap” to each LB and DT/DE. For those who aren’t familiar with gaps, here is a little graphic I made to illustrate:

So, when you hear someone say “A-gap blitz”, it means that a rusher (usually an ILB) will blitz between the center and the guard.

Techniques, on the other hand, correspond to where a defensive lineman will line-up on a given play.

If a DL was lining up at the 5-tech, it would mean he was lining up on the outside shoulder of the tackle.

In the 4-3 under, LBs and DT/DEs are each responsible for only a single gap.

This is to help players play more quickly and instinctively, rather than making them read and react to the offense. This is different than, say, a 3-4 defense, where the defensive ends are responsible for 2 gaps on any given play.

First off, let me show you the more historic, run-centric version of the 4-3 under.

In the original 4-3 under, the team employs four down linemen and three standing linebackers, hence the 4-3 name. It differs from the 4-3, however, in that the defense plays staggered to the weakside of the offensive formation. Hence the term “under”.

In this formation, the SAM (strongside outside linebacker) is lined up closer to the line of scrimmage on the outside of the tight end.

He’s responsible for the “D” gap, and he’ll also cover the TE depending on the coverage scheme. The strongside DE is lined up in the 5-technique alignment, and will be responsible for the strongside “C” gap.

Next to him, the strongside DT is lined up at the 1-tech, a position most commonly referred to as the nose tackle (NT). He’s responsible for the “A” gap on the strongside of the formation.

The weakside DT is often referred to as the “under tackle”, and is lined up at the 3-tech. He’s responsible for the weakside “B” gap. The weakside DE is lined up on the outside of the tackle, and is responsible for the weakside “C” gap.

As you can see, this leaves two gaps open: the strongside “B” and the weakside “A”. These gaps will be covered by the MIKE (middle LB) and WILL (weakside LB), respectively.

Take a look at the difference between this and the standard 4-3 alignment:

The standard 4-3 does not “stagger” to one side of the formation, and the LBs tend to play farther from the line of scrimmage. It also generally uses two smaller, lighter DTs than the DT/NT combo employed by the 4-3 under.

And here’s what the base 3-4 defense looks like:

The standard 3-4 also does not “stagger” to one side or the other. However, it does utilize the big NT to occupy two blockers, similar to the 4-3 under. It also tends to use big OLBs that are capable of rushing the passer, something that the 4-3 under will begin to use.

This basic version of the 4-3 under has been historically successful at stopping the run. But, in an effort to create more pressure on the QB, the scheme was changed slightly.

Teams wanted to create more mismatches against opposing offensive linemen, so the weakside DE was allowed to move around the formation and to rush the passer with his hand in the dirt and standing up.

Initially called the “Elephant”, but now known more commonly as the “LEO”, the weakside rusher was charged with getting to the QB and controlling the weakside “C” gap. Here is a look at the 4-3 under defense with the LEO rusher inserted:

This is the defense that Carroll and Quinn used to such great effect in Seattle. The alignment is essentially the same, with a few small changes.

Noticeably, the SAM backer tends to play a little closer to the line of scrimmage, and the FS tends to play a little further back. The LEO replaces the weakside DE, and he tends to play a little further off the weakside tackle.

I will be going into more detail on which players could fit at which position after the Falcons have drafted their (hopefully) pass rusher of the future, among other things.

But for now, I’ll give you a brief explanation of what each player in the front-seven is expected to look like and do in the 4-3 under defense.

LEO: The LEO is generally a player that is smaller than a DE but bigger than an OLB. He is expected to rush the passer well, as well as control his gap and take on other responsibilities (such as coverage) from time-to-time.

Quinn and Carroll have tended towards using lighter, more athletic players at the position in recent years, like Bruce Irvin. Potential Fits: Kroy Biermann, Tyler Starr, Prince Shembo, Stansly Maponga, O’Brien Schofield.

SAM: The SAM is generally a big, athletic LB that is stout in run support but agile enough to cover TEs and RBs when called upon. Potential Fits: Brooks Reed, Prince Shembo, Jacques Smith, O’Brien Schofield.

WILL: The WILL is the tackling machine of the defense and needs to have the range and athleticism to move across the field quickly.

Generally, the WILL is a lighter LB with speed that can blitz and cover in a pinch.

Sean Weatherspoon was an excellent WILL, and it’s a shame the Falcons let him get away (assuming he can stay healthy). Potential Fits: Justin Durant, Paul Worrilow, Joplo Bartu, Marquis Spruill.

MIKE: The MIKE is generally the defensive signal caller and leader of the defense. He should possess good football IQ and instincts, and he should be a player that never has to leave the field.

That means he should be adequate in coverage and run defense, and being able to help out as a blitzer is certainly helpful too. Potential Fits: Justin Durant, Paul Worrilow, Brooks Reed, Marquis Spruill.

Weakside DT (3-tech): The 3-tech DT is your penetrator and your best interior pass rusher. He also needs to be able to hold up in run defense.

Generally, he’s a lighter, more athletic DT that specializes in getting into the backfield and disrupting/sacking the QB. Potential Fits: Jonathan Babineaux, Ra’Shede Hageman, Cliff Matthews.

Nose Tackle (1-tech): The 1-tech NT is your stout, big, space-eating run defender. He will be expected to take on multiple blockers on every play and clog up the middle. His primary duty is stuffing the run, but being able to push the pocket is always a plus. Potential Fits: Paul Soliai, Ra’Shede Hageman.

Strongside DE (5-tech): The 5-tech DE generally plays like a 3-4 DE: a big, athletic player that is stout against the run. He’s generally a powerful player that is capable of taking on blockers and shutting down runs that come to his side.

In passing situations, the 5-tech might be switched out for a pass rushing 4-3 end. In Seattle, they used Red Bryant at the position for a time, a player whose game is very similar to fan punching-bag Tyson Jackson. Potential Fits: Tyson Jackson, Adrian Clayborn, Malliciah Goodman.

As you can see, the Falcons actually already have the personnel to run this scheme effectively.

They could absolutely use upgrades at several positions, namely the LEO and MIKE, but they have players (and depth) to immediately put this scheme into play.

It’s likely that Quinn will use the 4-3 under, but that won’t be the only scheme the Falcons run.

There will be nickel packages, “Bear” fronts (which I will cover in a later article), and a good deal of standard 4-3 and 3-4 mixed in. Quinn is a creative guy, and I’m sure he’ll put our players in the best position to succeed.

Stay tuned after the draft for more in-depth articles on the Falcons schemes and how the new players will fit into Quinn’s defense.

What do you think about the 4-3 under? Do the Falcons have the players on roster to make it work? Will the more simplistic, 1-gap approach make a difference?