In today’s installment of the “NFL 101” series, former NFL defensive back Matt Bowen breaks down the basics of the 3-4 defensive front to give you a better understanding of the pro game.

Click here for a breakdown of the 4-3 defensive front.

The 3-4 defense consists of three defensive linemen (two defensive ends, one nose tackle) and four linebackers (two outside linebackers, two inside linebackers).

But unlike the 4-3 fronts we talked about last week (Under/Over), these 3-4 defensive linemen aren’t built to use speed/quickness to penetrate the gaps/edges of the line (such as the 3-technique defensive tackle or the rush end in the 4-3).

In the 3-4 front, you want to think of size and length along the defensive line (J.J. Watt, Haloti Ngata) with the ability to occupy space/offensive linemen.

That frees up the inside linebackers and allows them to run to the football while the two outside linebackers (the premium position in the 3-4) make plays as edge defenders out of a stand-up, two-point stance.

Here is a quick look at the alignments (or techniques) of the three defensive linemen (plus the run gaps) in this diagram:

The defensive ends (in a base 3-4) align in a “5-technique” with the nose tackle in a “0-technique.”

In the traditional, old-school 3-4, the three defensive linemen will use a “2-gap” technique (play two gaps), but as you will see when we break down the multiple 3-4 fronts, there are variations of the defense that will use “1-gap” principles.

These are the 3-4 fronts we will look at today using the chalkboard diagrams and examples from the All-22 coaches tape:

3-4 Okie Front

The 3-4 Okie is that traditional, old-school front we see from teams such as the Patriots with both defensive ends and the nose tackle using a “2-gap” technique (play two gaps in the run front).

Inside, your two linebackers (Mike/Jack) should have the size to get downhill and fill in both the A/B gaps versus base runs with the two outside linebackers (Sam/Will) playing contain (or force) and cutback/boot.

As you can see in the diagram, the defensive ends (E) are aligned over the offensive tackles (5-technique) and are responsible for playing the “2-gap” in the B and C gaps. The nose tackle (N) is aligned head-up versus the center (0-technique) and must play both A-gaps.

At the second level, both inside linebackers, Mike (M) and Jack (J), align over the “bubbles” (uncovered offensive lineman) and fill in the A/B gaps. On the edge, the Sam (S) is aligned in a 7-technique outside the tight end (Y), and the Will (W) is in a 6-technique.

Now, let’s check out the alignments of the 3-4 Okie front using the All-22 tape of the Patriots versus the Buccaneers’ Regular/21 personnel (2WR-1TE-2RB) out of a Pro Strong I formation.

With the defensive ends and nose tackle (Vince Wilfork) in their traditional 3-4 alignments (5/0 techniques), the two outside linebackers are on the ball in an open (weak) side 6-technique (Will) and closed (strong) side 7-technique (Sam).

That leaves the two inside linebackers aligned over the guards (Mike/Jack) to fill downhill versus the base run game (Lead Closed, Power O, Counter OF, etc.) to the A/B gaps.

In the Okie front, you should expect defenses to blitz and use stunts (defensive ends slant, “X” stunt with outside linebacker, etc.) to take pressure off the two inside linebackers who are uncovered (and unprotected) from both guards.

3-4 Eagle Front

The 3-4 Eagle is a front you will see from the Steelers, Packers and Redskins. A “1-gap” scheme with the Sam ‘backer using the “2-gap” technique over the tight end to the closed (strong) side of the formation.

Looking at the diagram, both defensive ends (E) align in a “4i” (inside shoulder of the tackle) and play the B-gap with the nose tackle (N) working to the “front side of flow” (or the A-gap).

And because of the “4i” alignment of the defensive end to the closed (strong) side of the formation, the Sam ‘backer (S) now has to play a “2-gap” technique aligned in a 6 over the tight end (Y). He will press/flatten the tight end on the stretch play (can’t get reached) and also fill in the C-gap with the end now occupying the B-gap.

At the second level, both the Mike (M) and Jack (J) play “A-gap to scrape” (attack A-gap or scrape versus flow) with the Will (W) responsible for cutback/boot to the open side as a 6-technique.

Here’s how the Steelers aligned in the 3-4 Eagle versus the Bears' Pro Strong I formation out of Regular/21 personnel (2WR-1TE-2RB).

With the Sam head-up over the tight end (6-technique) and the ends in the “4i” alignment, the outside linebacker will use that “2-gap” to flatten the edge or fill inside the C-gap.

And as we talked about above, with the nose tackle working to the front side of flow (closed-side A-gap in this diagram), both inside ‘backers (Mike/Jack) will play “A-gap to scrape.”

A common question: Why do you align the ends in the “4i” technique when you play an Eagle front? This prevents the guards from gaining a leverage position to block out, and it also allows the ends to beat the tackle inside and chase versus the guard pull (Power O, Counter OF).

3-4 Under Front 

The 3-4 Under was a common front run by the Texans and defensive coordinator Wade Phillips during the 2013 season in Houston.

Another “1-gap” scheme that gives you protection to the closed side (four defenders) with the open-side Will ‘backer and defensive end in a position to clean up as cutback players.

To the closed side, the defense is protected with the nose tackle (N) in a 0-shade (or 1-technique) on the outside shoulder of the center (same as a 4-3 Under front), the defensive end (E) in a 5/6-technique and the Sam (S) is aligned outside of the tight end (Y) in a 7-technique.

And with the Mike (M) filling to the B-gap, the defense has every gap accounted for to the closed side of the formation.

To the open side, the Will (W) plays the cutback/boot from the 6-technique with the defensive end (E) aligned in either a 2- or 3-technique. The defense can align the end in a 3-technique (B-gap) with the Jack filling to the A-gap. Or, the defense can bump the end down to a 2-technique. This allows the end to “2-gap” the guard with the Jack (J) on a fill/scrape.

Let’s take a look at the 3-4 Under from the Texans versus the Raiders' Pro I formation out of Regular/21 personnel (2WR-1TE-2RB).

The first thing you should notice in this 3-4 front is the alignment of the nose tackle. Instead of being aligned head-up over the center (Okie front), the nose is now in a shade (or tilted) to the closed side of the formation with the defensive end (J.J. Watt) in a 5-technique and the Sam in a 7-technique.

The open-side defensive end is on the outside shoulder of the guard (3-technique) in the B-gap with the Will playing cutback/boot on the edge and the Jack filling inside to the A-gap.

However, as I said above, you can bump that open-side end down to a head-up position on the guard (2-technique) and allow him to “2-gap.” That gives the end a “two-way-go” with the Jack linebacker filling from the second level.

3-4 Personnel Fits

If you want to build the perfect 3-4, you need the proper personnel. Here’s what you should focus on when looking for the ideal skill set/size to produce out of the 30 front.

-Outside Linebacker

The premier position in the 3-4, the outside linebacker has to show the ability to rush off the edge, close the formation (or hold the point) versus the strong-side run, make plays as a cutback defender and also display the athleticism to drop into coverage. Power and speed on the edge of the defense. 

Think of the 49ers' Aldon Smith, Packers' Clay Matthews or Colts' Robert Mathis at the pro level with Buffalo's Khalil Mack, UCLA's Anthony Barr and Auburn's Dee Ford as the top prospects in this year's draft class. 

- 5-Technique Defensive End

Size, length (reach) and strength to play the “2-gap” technique versus offensive tackles with the athletic ability to align as a “1-gap” defender. These players are space-eaters who keep blockers from getting to the second level while also disrupting protection schemes up front.

The Texans’ J.J. Watt (6’5”, 290 lbs), 49ers’ Justin Smith (6’4”, 285 lbs) and Jets’ Muhammad Wilkerson (6’4”, 310 lbs) are prime examples of 5-technique defensive ends with the ideal skill set/size to produce at the position in the NFL game.

Looking at the draft, I would focus on Missouri's Kony Ealy (6'4", 273 lbs), Notre Dame's Stephon Tuitt (6'6", 304 lbs) and Minnesota's Ra'Shede Hageman (6'6", 310 lbs). 

- Nose Tackle

The nose tackle in the 3-4 is the anchor. That means size, strength and core power to command double-teams and keep the interior guards off the inside linebackers. The nose has to be quick off the ball and play with leverage.

In today’s game, I’m looking at players such as the Ravens’ Haloti Ngata (6’4”, 340 lbs) and the Browns’ Phil Taylor (6’3", 335 lbs). Players who have the size/strength to win matchups at the nose tackle position.

And in the draft, keep an eye on Notre Dame's Louis Nix (6'2", 331 lbs), Florida State's Timmy Jernigan (6'2", 299 lbs) and LSU's Ego Ferguson (6'3", 313 lbs). 

Up next in the “NFL 101” series: Breaking down the NFL Route Tree

Seven-year NFL veteran Matt Bowen is an NFL National Lead Writer for Bleacher Report.