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Football 101: Intro to Defense Terminology

MHR University is back with an intro to defensive terminology in the NFL. From defensive line to coverages, we break it down here.

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Denver Broncos v Atlanta Falcons
A defensive overview for life under Vic Fangio.
Photo by Joe Robbins/Getty Images

One of the issues that has been brought to my attention a number of times since I started at Mile High Report are questions regarding certain techniques, coverages, and alignments. It’s easy to forget how much lingo is involved in football when you spend every day studying it, but the point of entry can seem overwhelming with a culture shock of sorts.

Throughout the last year, bits and pieces of the following terminology have been covered here and there, but never as one syllabus to serve as a sort of one-stop shop to be reviewed as it serves you. Here, I’ll cover some terms you’ve probably encountered before, but may not have entirely understood.

Welcome to class.

Defensive line techniques

On the surface, it seems easy enough to say Khalil Mack and Von Miller are both edge rushers, while Shelby Harris, Derek Wolfe, DeMarcus Walker, and Dre’Mont Jones are defensive linemen. This accurately summarizes the positions they play, even if there are noticeable differences in their skill sets.

I’ve talked before about how Harris’ responsibilities will change in 2019 because he’ll play more snaps at the 2i and 3 technique in addition to his role as a nose tackle (0,1). The responsibilities for those roles is quite different. This post by Pro Football Focus does a good job explaining.


This is the nose tackle. This player will line up directly over the center and historically has been tasked with two gaps against the run. This player could also be a one gap player who will shoot a gap.

If the nose is playing two gap, on the snap they are expected to diagnose the blocking scheme and defend the more vulnerable gap. A two gap defensive linemen takes on blockers instead of working to penetrate the line of scrimmage. The rationale is that this will free up others to make plays.

You can read more about the difference between one gap and two gap play here.

Bilal Nichols (98) lined up as a NT.


This is the first area of confusion among some fans, as the 1-technique is also considered a nose tackle. The key difference between the two noses is that the 1 is shaded to one side of the center and he’s generally a one gap player. This means he’ll be asked to shoot one gap instead of waiting and playing to whatever gap he needs to protect post-snap.

Because of the alignment, 1-techniques will still soak up a lot of double team blockers, which helps other players to get one-on-one matchups.

Eddie Goldman (91) lined up as a 1T.


This lineman is typically the star pass rusher, as his primary responsibility is to shoot the B-gap and make plays on the opponent’s side of the line of scrimmage. This alignment is used to provide more one-on-one opportunities, as it’s difficult for an offensive tackle to assist on this player since he’s typically responsible for blocking an edge rusher.

Akiem Hicks (96) lined up as the 3T.


In a base 3-4, this is the defensive end. The 4i, 4, and 5-technique are lumped together because these responsibilities have a lot of overlap. 5-technique tends to be the umbrella term for these players, even though it’s the little used alignment of the three.

Historically, the 5 technique defensive end is most often utilized in a similar way to the 0-technique nose. Aligned across from the offensive tackle, his job on running downs is to defend whichever gap is more vulnerable post-snap. In recent Broncos history, Derek Wolfe has played this role to tie up blockers for Von Miller to rush the passer.

Realistically, the use of this technique will go down in the Fangio defense, as the Broncos will employ more sub-packages.

Derek Wolfe (95) lined up as 5T while Adam Gotsis (99) lines up as 4T.


The primary responsibility against the pass here is to collapse the pocket. When lined up head up on the tight end, this player is usually meant to jam and/or reroute the tight end before he rushes the quarterback. Against the run, this guy is asked to set the edge and funnel the ball back inside.

Read more about the technique here and here.

Bradley Chubb (55) lined up at 6T.

Wide 9-technique

After the 3-technique, this is probably the most widely understood assignment among casual fans. These players line up far outside the offensive tackle and rely on speed to beat their blockers around the corner and get pressure on the quarterback. This should sound familiar to Broncos Country, as Von Miller has been the prototypical wide-9 for a number of years.

You can read more about the wide 9-technique here.

Von Miller (58) and Bradley Chubb (55) lined up as wide 9s.

One of the obvious benefits to understanding the aforementioned techniques is how you can start to see the vast differences between Vance Joseph’s 3-4 and Vic Fangio’s. Because Fangio uses more nickel personnel, there is a lot of emphasis on a player’s ability to line up at 3 technique rather than 5.

This is why Dre’Mont Jones made a great deal of sense in the 3rd round of the 2019 NFL draft. Coming out of Ohio State, he was considered a pure 3-technique, and he’s short for a 5-technique.

It’s also important to mention that even if Jones was drafted to be an interior rusher, he’ll play other techniques. Most defenses change up alignments from down to down in order to make it more difficult on blocking schemes. Vic Fangio has mentioned before how it’s crucial for guys to play multiple roles.

I invited fellow MHR writer Jeff Essary to expand on the topic:

Retweet everything that was said above and I would add one caveat to keep in mind: I think the important thing to recognize with fronts and techniques is that we as fans are pretty quick to bucket guys into a prototype based on where they line up, when in reality, there are essentially two overarching buckets that guys will typically fall into - Edge and Interior DL - and you could be asked play any one of the above techniques on any given down. For instance, Gotsis, Wolfe, and Shelby Harris all played up and down the line and rotated back and forth between 3, 4, 4i, and 5 techniques in base fronts, often on the same drive.

Also, lines are even blurring between edge and interior players as guys like JJ Watt, or Aaron Donald at times, are lining up in Wide-9 and getting after the quarterback in certain sub-packages.

The best coaches will put guys in the best position to be successful, and sometimes that looks like a specific niche or technique for some guys, and sometimes it looks like moving guys all up and down the line because they can do that.

While Fangio will generally keep guys in a certain lane in terms of roles, he falls into the latter category with his defense. If you’re an interior player for him, expect to line up anywhere from the 0-7 techniques on any given snap, depending on the personnel, and what the offense is trying to do.

Gaps and Run Fits

(Jeff Essary - updated)

You’ll often hear coaches and players talk about things like “shooting the gap”, “gap integrity”, or “filling their gap” when discussing run defense.

At it’s basic form, playing run defense is about ensuring you have a defender responsible for every “gap” between an offensive lineman or blocker in a run play. Similar to the techniques, there’s a sequencing system that starts at the center and works out in either direction using letters.

The spaces on either side of the center in between the center and the guard are the A-gaps, in between the guard and tackle are the B-gaps, and outside the tackle are the C-gaps. They go on further if the offense has a TE or anyone else on the line.

You’ll often hear the gaps referred to in blitzes as well. A “double A-gap blitz” is when two blitzers rush through both A-gaps, the spaces on either side of the center.

The next piece of the puzzle is maintaining “gap integrity” or your “run fit”. This is essentially every defender’s gap responsibility on any given play if the offense happens to run the ball.

Now, the amount of defenders that the defense commits to fit the run, meaning they have a specific run defensive assignment, will depend on how many gaps the offense has to defend.

If the offense comes out with one tight end like you see below, that means the offense technically has seven gaps to account for, so that’s the minimum number of bodies they would need to have run assignments, or “fit” a gap at the start of the play.

As an aside, this is another reason coverage for linebackers and at times safeties is so difficult. Aside from athletic hindrances, they often have to split their attention between maintaining gap integrity, at least at the start of the play, and also getting to their coverage spot or matching up with their man. This is how coverage affects run defense and is what connects the back end to the front seven.

Let’s take a look at how this plays out below. Currently, Denver is in nickel with four linemen and two linebackers. We counted before that there are seven gaps to cover, so Darian Stewart will be responsible for one from his strong safety position.

Right now Denver is fitting this play properly. All the gaps are accounted for. However, trouble ensues when the Jets motion a receiver over.

You can see below, the linebackers have shifted over, as they must have been expecting the safeties to switch, now that there are two wide receivers on Stewart’s side, perhaps they expected him to rotate up high and Simmons to come down into the box.

Somewhere, wires were crossed, and Stewart is stuck in no man’s land trying to figure out what’s going on and the C gap is wide open with no one covering it. The Jets would pick up 54 yards on this play because of this error.

Now that’s just a super simple rundown conceptually, and an example of how the secondary and the front seven must be on the same page.

For more complex looks at this, check out Coach Cody Alexander’s stuff on He has some great pieces on how you fit the run against spread looks, or against trips, etc.

The last nuance on this, which “Coach A” digs into a lot is how defenses can protect their players by aligning their coverage responsibilities closely with their run fits. You’ll hear the term a player is “in conflict” referring to players that have both run responsibilities in a certain gap, but also have coverage responsibilities that take them away from that.

In the below, graphic, the defense’s issue is the Mike linebacker is in conflict. He has to defend the A-gap in the running game, but also relate to the #3 receiver in coverage.

That’s a lot of ground to cover, and you’re just asking to get picked on in play action or with RPOs.

In the graphic below, the defense remedies this by shifting the line so that the defensive tackle is taking the A-gap, and the Mike now has the B-gap, a much easier responsibility to reach while allowing him to shade the #3 receiver.

Notice to do that, the defense has to borrow a safety on the backside. This safety is now in the run fit. Check out the link for a deeper dive.


Before we dig in on the secondary, if things like “man” and “zone” coverage are completely alien to you, I advise you check out this link. No shame, we all start somewhere. After all, back when I was 13 years old, I spent my allowance on Football for Dummies and read it cover to cover.

Anyway, a big difference coming to the Broncos under Vic Fangio is found in the secondary. The Vance Joseph and even Wade Phillip Broncos were notorious for their reliance on man-to-man coverage. Last year, Denver used man coverage more than every team save for the New England Patriots.

Back to the Broncos, this may not change a great deal. According to Sports Info Solutions, Fangio’s Bears used man-to-man 44% of the time.

However, like the defensive line discussion above, it’s important to note how simply stating man-to-man vs zone misses the trees for the forest. Without diving too deep into the weeds, these are a couple of the big changes that are coming to the Broncos’ secondary:

Middle of the Field Coverage (MOFC)

Dating back as far as I can remember, the Broncos have played the vast majority of their snaps out of MOFC shells. This means there are 8 players near the line of scrimmage and a clear free safety playing in the deep middle.

If there’s a safety in the middle, it’s MOFC.

On a basic, fundamental level, one big reason teams will play MOFC is to bring an eight defender near the line of scrimmage to assist against the run. As personnel has gotten lighter and more one gapping has been deployed, this has taken on even greater frequency.

While every NFL team changes their coverage and utilizes different rules and responsibilities, the vast majority use MOFC on most downs.

Obviously with the way NFL defenses use deception post-snap, what you see pre-snap is not always the case after the quarterback has the ball, but these are common coverages based out of MOFC and where you can read more:

  • Read more about Cover 1 here.
  • Read more about Cover 3 here.
  • Read about pattern match Cover 3 here.

Middle of the Field Open (MOFO)

Under Vic Fangio, the Broncos will utilize more coverage shells considered Middle of the Field Open, or MOFO.

If there isn’t a safety in the middle of the field, it’s considered MOFO coverage.

One big reason for this is because Fangio utilizes quarters coverage, or Cover 4. As offenses trend more and more into spread and air raid concepts, Fangio has found this to be the most effective way to combat it. It’s also extremely flexible.

At it’s most basic level, “quarters” is a four-deep, three-under zone defense that looks a lot like man coverage. Depending on the route combination, it’s possible for both safeties to double up on receivers, which is called a bracket.

Where Fangio and other C4 schemes have grown from the basics is how the pattern matching has evolved. As Jeff Essary mentioned here, Fangio’s defense can cut the field in half to play one coverage on one side of the field and an entirely different coverage with a different set of rules on the other.

It can be hard to break down pre-snap, but another coverage off of Cover 4 that many MOFO coverage shells lean on is what’s called Cover 6. When this happens, the coverage is Cover 4 to one side of the field and essentially Cover 2 to the weak side.

As I mentioned before, with the way NFL defenses use deception post-snap, what you see pre-snap is not always the case after the quarterback has the ball, but these are common coverages based out of MOFO and where you can read more:

  • Read more about Cover 2 here.
  • Learn more about 2-man here and here.
  • Read more about Cover 4 here.
  • Read even more about Cover 4 here, here, and here.
  • Read about Cover 6 here.

If you’re looking to dive into more specific details on how Fangio will impact coverages, Mile High Report’s Jeff Essary covered it here and here.

JE: Joe put it perfectly above. One additional nuance is that with a multiple defense like Fangio’s, it can sometimes be hard to classify the coverage at first glance. Sometimes there will be a mix of zone match with one man designated in MEG (Man everywhere he goes) coverage on the outside receiver, or the defense is in split field coverage, but kicks the backside safety into the middle of the field based on offensive alignment so it looks like Cover 3, but is actually a variation of split field coverage.

All that to say, as it relates to Fangio’s defense, when you hear the coverages Joe listed above, think of them more in terms of coverage shells, as he mentions, with a myriad of variation underneath that depending on what the offense is doing, as opposed to a static coverage with the typical responsibilities you would anticipate within each of those.

Lastly, if anyone has NFL Gamepass, I highly recommend Steve Spagnuolo’s segment on basic coverages, and any of their player film segments, as they are a great way to learn the fundamentals of the game from the practicing pros.

Please let me know if you have any additional questions and I’d be happy to try to answer them.