Fundamentals : 4-3 Defense (Base, Over, Under)

football, defense, basics

*Due to massive interest, this post is in the process of being rewritten and featured as a series for the 2014 season. In the meantime, please read the comments section as it is tremendously helpful! Thanks to everyone who has reached out about the post so far. Keep any comments coming!

This Fundamentals post serves to answer a question I’ve had for just about forever: what’s the difference between base, over, and under?

So I found the answers and turned them into color coordinated pictures. Because that’s what we do around here.

Ok, ready?! Here are a few foundational truths to lay out before we get rolling with this:

  •  Base defense refers to the default defense that a team runs as a standard. For most teams in the NFL, their base defense is either a 3-4 or a 4-3 defense. Think of base defense as an empty room with a table and chairs: there will always be the same number of furniture pieces in the room, but you can rearrange them in any way that suits your needs. In the same way, teams that run a 3-4 defense as their base defense are going to field 3 linemen and 4 linebackers, but they can rearrange them in different ways if need be. 
  • Over and Under Fronts describe how players are aligned within a base defense. In an over front, the four-man defensive line aligns to the strong side of the offense (the side with the tight end). In an under front, the defensive line aligns to the weak side (the side without the tight end). There can also be over and under fronts in 3-4 defensive systems, in which an outside linebacker would move up to become the 4th lineman. (Thank you so much for your help with this correction to the original post, Drew and Curtis!)
  • Ok, this is going against everything we’re learned so far, but sometimes there is a nose tackle in a 4-3 defense. It’s true. I’ve been withholding information to make the learning process between 3-4 and 4-3 easier, and now I kind of feel like I just told you all you were adopted. So, here’s the thing: the nose tackle in a 3-4 system in the sole defensive tackle and plays 0-technique. We know that. In a 4-3, a nose tackle (if used) would usually have about the same size and strength as a traditional nose tackle, but would play 1-technique instead of straight over the center in 0-technique. According to Pat Kirwan, “A 4-3 nose tackle is required to penetrate the inside “A” gap and often loop around and be responsible for containing the “C” gap.” (See this post for a refresher on gaps.)

Now that we have the basics ironed out, let’s move on to what a 4-3 base defense might look like.

(For all of the following illustrations, W = weakside linebacker (Will), M = middle linebacker (Mike), S = strongside linebacker (Sam). Remember that the strong side of any formation is the side with the tight end; the weak side is the side without the tight end. Check out the glossary for more help with these positions.)

football, fundamentals, defense


We won’t spend a lot of time here because we already know this defense fairly well. In a 4-3 Base Defense, there are 4 defensive linemen and 3 linebackers. Usually, they are aligned in a formation similar to the one above, but certainly not always.

Let’s stick with the 4-3 Base and see what an over front would look like:

football, fundamentals, defense

In the 4-3 Over Front, the defense shifts it’s strength to the strong side of the offense. How can that be, you ask, when there are more defensive players on the weak side than on the strong side? Great question! It’s all about the defensive tackle.

We see that the nose tackle is lined up on the weak side of the formation. And he’s important – his size and strength will plug up the gaps like nobody’s business. But the crux of the Over/Under fronts is built around the abilities of the defensive tackle.

In the Over front, the defensive tackle is aligned on the strong side of the formation. That defensive tackle is usually a 3-technique player. We know that the 3-technique player is aligned on the outside of the guard and relies on speed and agility, rather than sheer size (ala nose tackle), to shoot the B-gap and disrupt the backfield. The defensive tackle is the true “strength” of the formation and wherever he is will be the side to which the defense is shifting it’s strength. When the defensive tackle is on the strong side of the formation, it’s a 4-3 Over front.

football, fundamentals, defense

Since you guys are all A+ students, I’m sure you are all anticipated what comes next: In a 4-3 Under Front, the defense shifts it’s strength to the weak side of the offense. See where the DT is? 3-technique on the weak side. A lot of NFL teams runs this defense because the defensive tackle has less obstacles between himself and the backfield. As long as he can shoot the B-gap he can get into the backfield and disrupt the action.

It’s a little counterintuitive to remember that the strength of the defense is the side that has less players and a little confusing to untangle the strength of the defensive from the strong sides and weak sides of the offense – I’ll give you that. But in general, now that we understand the role of the defensive tackle in all  of this, does it make more sense?

Shout out your questions, comments, and concerns!

Author: Beka