The 4 Most Important Aspects of the Under Front Defense


The 3-4 or 4-3 under front defense is popular, especially versus 21 personnel. In my opinion, there are 4 critical elements of the defense that as a defensive coordinator, you need to know them as your strengths. As an offensive coach, you can try to break down for some success.

Under Front Defense: The Tandem

The tandem is one of the 4 most important elements of the under front defense. The tandem basically is the outside alignment on two adjacent linemen on the end of the line of scrimmage. Versus 21 personnel sets, you get this to both sides. If you are going up against a 5 man line of scrimmage, you will only have it to one side, but you will still have leverage with a linebacker likely apexed (splitting the difference) with the tackle and the slot. If it’s trips, you still probably have leverage.

The Tandem

Here the End and tackle to the left and End and Sam to the right make the Tandem.

The Tandem basically protects the outside edges of the offense from attack in the under front defense. From an offensive perspective, you can attack the tandem by down blocking on the interior defender, but that will likely lead to a gap exchange, which I will explain later.
Because the gap exchange takes a second to fully complete, some offenses, like the Wing-T, will sometimes execute cross blocks, where the interior blocker executes a very short pull, almost like a trap, on the outside defender. The exterior blocker blocks down on the interior tandem player first.

Arc Option versus Under Front Defense

Attacking the Tandem with the Load Option. Courtesy of

This strategy can pry open then tandem. The two under front defense linebackers may flow over the top of the gap then, or have to play in a relatively unknown position.

Overall though, the tandem is a hard to break advantage for the Under front. It can protect less athletic players and give the defense a good edge. It also protects the linebackers so that they can pursue outside if need be.

Under Front Defense: The Safeties

Another important element of the 3-4 or 4-3 under front defense is the play of the safeties. They need to be aggressive in supporting the run because there are really only two true linebackers in the box (aligned usually in 30 techniques over the guards and about 4-5 yards back).

They need to be active to help support the run to one side and prepare to help in gap exchanges if the defense calls for it. They need to be the force players in many coverages, ensuring that the the play doesn’t get outside.

At the same time though, they need to be adequate pass defenders. This is why I like more athletic safeties. These players won’t be taking on bruising backs very often, but they need to be well coached and disciplined so they can identify play action, but they should be athletic so they can quickly support the run or the pass (or recover on play action).

The safeties should make calls like, “I’m here”, to tell the linebackers that they can help support the run. They can usually do this when they’re not forced outside by a slot receiver, with the exception being a loose deep half zone coverage technique.

For offenses, I’d challenge safeties with sweep and outside zone plays and play action passes. Make them move around. In addition, option plays, even two man option plays like speed or load option, will challenge these defenders. If you can build play action off of these routes, you’re in business.

The Under Front Defense: Gap Exchange

I won’t touch too much on this principle since you can read about football’s gap exchange here. But the basic principle is that if an offensive blocker, especially on the edge, blocks down, the player outside of him will step down. That defender will get hands on the blocker to keep the blocker from getting to the linebacker. The linebacker will hustle down to the line of scrimmage, keeping his shoulders square.

Under Front Defense Will Linebacker Gap Exchange

Will Linebacker Replaces End to Steps Down With Block

The under front linebacker should be able to reach the defender he’s exchanging gaps with. For instance, if the Will replaces the end in the gap exchange, he should be able to reach out and literally touch the end as he’s stepping down. This ensures the gap exchange is tight and quick.

Teams the gap exchange can be exploited by using that action against them. Use constraint plays to make the defense wrong. This could be as easy as play action power where the fullback leaks into the flat quickly and everything else looks like Power-o. Create doubt in the defense and use this strategy against them.

The Under Front Defense: The Will Linebacker

The Will linebacker needs to be an athlete in the under front defense. He is pivotal for it’s success (and as such, the three technique infront of him deserves a lot of credit – as does the nose and 5 technique end). But the Will linebacker is protected by those 3 defensive linemen. His direct gap, the A gap, is hard to get to with a good nose and three technique. If those two players can’t secure that A gap by size and strength, stunts can discourage the offense from attacking that gap. In addition, a well coached will linebacker who was taught by some great high school linebacker drills couldn’t hurt either.

The will linebacker can be undersized, but he must have great instincts and a sense for the ball. He’s setup to make plays. Because his gap is easily a “closed window”, he can flow and support other gaps well. I’ve seen many will linebackers in under fronts take over games.

I had the pleasure of helping to coach an offensive line against my cousin a few years ago, who played Will linebacker for that year’s state runnerup. Both of our teams were talented (this was basically a conference championship-esque game) and both teams made it deep in the playoffs. But he tore it up. He was well protected, and we did best running right at him. But he made plays all over the field because he fit this role perfectly. They ran almost exclusively the under front, and he could go sideline to sideline. Now, he wasn’t an amazing athlete, he got a NAIA scholarship, but he was often being recruited by D-III and some D-II schools if I remember. But he was an athlete as a linebacker in that defense, and that’s how I mean it. A 40 time won’t tell you anything. A better measure would be to get your film on and time the linebackers as they travel to their gaps.

The ending to this game totally sucked by the way... (Tied with 2 secs left, they block our field goal attempt and take it to the house. I was not happy).

The ending to this game totally sucked by the way… (Tied with 2 secs left, they block our field goal attempt and take it to the house. I was not happy).

The Will linebacker, because of his athleticism, can be attacked though. Run right at him in different ways. The goal is to get people on him to wear him out. I usually am not an advocate of this style of play calling, but if someone is a matchup problem, as a Will linebacker usually is b/c he can win on the way to the edge with the way this defense is built, then you need to make him work. Run weakside Isolation and Power plays in his direction. If your fullback can win one on one, run iso right at him until he wears out, then run in other directions.

Conclusions on the Under Front Defense

The Under Front Defense is a terrific look. I like the Over a lot at the high school level because it has three linebackers roaming, plus the two safeties, but the under front has a history I cannot deny.

If you’re looking to get a copy of an under front book, Jerry Gordon is the place to go. You can order his book from Amazon for about 13 bucks by clicking here.