AbsolutAnalysis: Defensive Fronts, Part One

Over the next week, Seahawks.NET will proudly re-publish select articles from Matt Lathrop, our "Xs and Os Guru"! We'd like to begin with his excellent three-part article on defensive fronts, part one of which was first published one year ago today.

I had a request in the "NET Premium Members Forum" to outline gap responsibilities for our defense, and figured I may as well present the basic fronts seen in the NFL, along with gap responsibility for each. Over the next couple weeks, I will look at the most popular fronts for a 4-3 defense, which includes Stack, Over, and Under, while touching on a basic 3-4 front, and throw in the classic 46 Bear defense. No one used the 46 anymore until the Baltimore Ravens decided to adopt it in 2005. It was a revolutionary defense that you will see "children fronts" of today. We'll go over that more next time, when I present a 4-3 Stack, Base 3-4, and 46 Bear. Today we will look at 4-3 Over and Under fronts.

Just to make sure we're all clear, 4-3 refers a front having 4 defensive linemen, and 3 linebackers. 3-4 then refers to 3 DL and 4 LB. Before we get into the fronts, below is an image that outlines the numbering system for defenses, in particular the DL. It's rather simple, but is necessary at every level of football. You may hear a "3-technique DT," and this is what is meant. He is lined up in the 3 position, outside shade of the OG. When using simple, multiple fronts, this makes it very easy to move your DT's, and even DE's if you wanted, around by simply calling in a couple numbers.


Now we can move on to the fronts, and how strong side and weak side runs are attacked from each. i.e. who has which gap and responsibilities. 4-3 Under and 4-3 Over are very common fronts, probably the most common in the NFL. Let's get to the diagrams, and start with an Under front.

4-3 Under Front

As you can see, just by checking the DT and NT you can assume that the defense is at least in a version of an Under front. Bringing the Sam to the line over the TE is another key, with the DE lined up outside shade of the Tackle. Inside, there is a Nose Tackle always lines up to the weak side 0, with the DT lining up in the strong 3 spot. Both Defensive Ends will line up in a 6, as the backfield strength is irrelevant to the alignment of the DL in an Under. The Sam is on the LOS, lined up in a 9 over the TE. The Will and Mike shift slightly to the strong side, as shown above.

4-3 Under vs. Weak side run

Rather than having set gaps regardless of the play, gap responsibility is determined by the side the ball is ran to. Assignments against a weak side run are displayed above. In the fronts presented today, the DT and NT have the gap they are lined up in, and either pursue the ball if it is ran to their side, or squeeze down one gap if ran away from. For example, in the diagram above, the NT attacks strong A gap, and pinches the weak A gap while protecting cutback by closing down backside lanes. However, the DT pursues the ball since it is run to the side of his gap. As you will see below, the opposite is true versus a strong side run. Here, the Sam is responsible for backside pursuit while protecting against cutback and reverse. In this base Under, Will must beat the ball to the outside and be the force on the defense, while the Mike has A gap responsibility and should be 2nd or 3rd to the ball behind the Will.

4-3 Under vs. Strong side run

As you can see above, the roles are essentially symmetrical to a weak side run. The Sam now has outside contain and force, while the NT and strong DE attack their gaps and get to the ball. Backside DL once again must pinch down their gaps one gap down and block off any cutback lanes. Mike has strong B gap to the ball, while Will is first accountable for weak A, before getting to the ball and cleaning up the play. Weak DE must pursue the play while protecting against reverse. Now, let's check out an Over front.

4-3 Over Front

As I mentioned with the Under front, the alignment of the DT and NT will key you to what the defense is running while you watch a game. In an Over, the DT will be lined up in a Strong 3, with the NT in a Weak 0, while the Sam will be in a Stack position, rather than up on the LOS. While an Over is not an exact flip of an Under, it is quite close to being symmetrical. The Will is up towards, if not on, the LOS, and the DE inside him is head up on the Tackle in a 5. The Strong DE replaces the Sam's Under position by lining up in a 9 on the TE.

4-3 Over vs. Weak side run

When taking on a weak side run, the Will once again is the primary force in a base Over front. However, the defense has one extra man on the weak half of the box in this front, which is much better suited for a weak side run. The weak DE may act as the force in some coverages, but whatever the role, he must not get hook blocked, meaning he cannot let the Tackle get outside of him and seal him off from the outside. Mike has weak B gap to the ball, and will be a secondary force to the play, arriving after the Will\DE primary. Since the ball is run to the weak side, the NT must control his gap and pursue the play, while the DT pinches down the Strong A, eliminating cutback lanes. Sam is responsible for Strong A to while getting to the ball. The DE lined up in a 9 must protect and contain against reverse and counter.

4-3 Over vs. Strong side run

I‘d imagine this diagram looks pretty simple by now. I'm sure you could have drawn this one up just by going through the previous fronts. Again, the DT is play side, so he controls his gap to the ball, while the NT attacks his Weak A while pinching down the Strong A since the play went away. Strong DE has primary force in this front, and must contain the ball, otherwise string the play out to the sidelines while waiting for secondary force to arrive in the form of Sam, the SS, and even a CB. Sam is responsible for the C gap while moving to the ball, and Mike slides in while preventing cutback by controlling the Strong A. Weak DE pinches down the Weak A while pursuing the ball and spying cutback. Will is assigned to pursuit while preventing reverse and cutback\counter.

That does it for this week, I hope you enjoyed the column. Remember that in the NFL, no front or scheme can only be used in one particular way - each coordinator has his touches and quirks to every scheme and front. But what was presented in this column should provide you with the basics of recognizing and dissecting what front is being run, and what each players responsibilities are. Next time we will continue the topic and look at a 4-3 Stack, as well as 3-4, and 46 Bear fronts. If you have any questions, requests, or comments, please feel free to email me. Any complaints or criticisms, email my boss.

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