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Defenisve Strategy: Linebacker Keys

The next entry on Clemson's base defensive alignment and its use of the triangle key

Kim Klement-USA TODAY Sports

Football is controlled chaos, and no position exemplifies such a contradictory term like linebacker. If a linebacker has to think, he is too slow to wreak havoc on an offense; if he plays with reckless abandon, an offense will easily take advantage of his freneticism. He must know his responsibilities before the snap so that a simple read at the start of the play tells him where to direct his fury. If done properly, we enjoy moments like this:

Boulware 4th down vs FSU

Welcome to part 2 in our offseason Brent Venables Discipleship class. Part 1 highlighted the defensive line in Venables' preferred 4-3 Over front. Part 3 would've explained Pattern Match Cover 4, but Dbbm reminded me he basically rewrote the New Testament on coverages last summer. LINKS APLENTY; PRAISE BE TO OCULUS:

Man CoverageCover 2Cover 3Cover 4Cover 6

So, I leave part 3 up to you Syracuse-loving commenters -- let me know what you want to read, and I'll trick you into believing in my expertise through an overabundance of gifs and big words. Here, however, we will discuss the multitude of responsibilities Clemson's linebacking unit must process and repeat until an assignment becomes instinctive. If my alleged expertise isn't enough for you, I consulted the up-to-date and foolproof wisdom of my 9th grade cousin, Griffin, who plays Rover in a 4-4 front for his high school team. Every 9th grader knows he's never been wrong about anything, and who am I to doubt such confidence? MODERN LINEBACKING ACCORDING TO A 9TH GRADER:

Q: Are you coached to read the offensive line or the running back?

I look at the guard at the snap, if he stands up to pass block I know it's a pass and I drop into the flat and watch the QB. If the guard run blocks, I look for the ball and the running back. If he runs away from me, I stay home and and prevent the reverse before I find the angle of pursuit. If he runs towards me, I set the edge and force him inside to my help. Then I SEE BALL GET BALL. Stay hype.

Q: So you were coached to read the triangle key?



You will recall that in Clemson's base 4-3 Over front, the defensive line shifts to the strong side, which leaves 3 "bubbles" or holes in the defensive front. It is the linebackers' responsibility to fill these holes, first and foremost, and generally align over their respective holes in what is called a "Tan-Zero-Tan" alignment: the outside linebackers align over the Tackles and the middle linebacker over the Zero, or nose.

4-3 over bubbles

This diagram showcases the linebackers' Tan Zero Tan alignment, but bear in mind that gap assignments vary by play call; this is only the most basic of assignments. For example, the 3 tech DT could stunt into the A gap and the Mike could bullet through the B gap. An offense could overload the strong side, shifting the linebackers into different alignments before the snap. No matter the call and alignment, every gap is always covered.

Against spread formations, a Sam linebacker is often split out like a third corner to cover a slot receiver or tight end. Sometimes, the Sam is altogether replaced by a third corner, known as the nickel (derived from the inclusion of a 5th defensive back). This does not remove a gap from the equation, it is simply displaced.

Nickel vs 113

What Clemson usually does, specifically, against 113 personnel is split the Sam/Nickel out wide on the slot receiver as I alluded to above. Then Clemson walks a safety down into the box to fill the open gap normally filled by the Sam. It is an aggressive tactic, one which Clemson frequently employed thanks to solid cornerback play outside and physically transcendent safeties in Jayron Kearse and TJ Green.

With Green in the box to fill the vacant gap, Clemson had enough bodies to fill each gap against the run and comfortably man up on the 3 receivers with 3 corners (as opposed to matching 2 corners and 1 safety on the 3 receivers in a 4-3). The point is no matter the formation, personnel, alignment, or call, every gap is always covered.

Read Keys

Linebacker is generally considered the hardest position for a defender to mentally grasp, not only because of the various gap and blitz responsibilities, but because after his initial gap responsibility he must drop into a zone or cover a receiver should an offense choose to pass. How does he know what to do at all, much less know it quickly enough to not bust an assignment? The answer, which Griffin alluded to, can be found in knowing where to look.

Simply put, a key is the "tell" a linebacker watches which will help him determine whether to charge his gap against the run or drop back to cover a pass. A linebacker may read a running back, which is fine in the event of a handoff, but could prove disastrous with play-action or any sort of counter motion. Or he could watch the offensive line, whose blocking will allow him to accurately determine run or pass, but is slow-developing and could freeze a linebacker into hesitancy.

What many defenses -- including both Clemson and Griffin's school -- teach nowadays is a combination of these two, known as the triangle key: a linebacker watches the guard and tackle closest to him plus the running back. The triangle is a compromise which incorporates the speed and aggression of a running back key with the accuracy of an offensive line key. It is still susceptible to play-action (we saw plenty of bites against play-action near the end of the regular season) but thanks to the guard and tackle keys it is not nearly as reckless as a simple running back key.

Keys vs counter

Above, FSU went back to the same counter run with which they gashed Clemson early. The player I want you to watch is Mike linebacker B.J. Goodson, who reads the counter when he sees the pulling guard (offensive line key), then flows to Dalvin Cook and attacks with speed (running back key) to makes the tackle.

Were Goodson to read only a running back key, he may have run himself out of position with Cook's first few counter steps away from the eventual play side. With only an offensive line key, Goodson's eyes may have been lost in the scrum and allowed the best running back in the country to zip past him.

Below is another example of the benefits of the triangle key, where Clemson's linebackers properly diagnose a screen pass to Cook:

keys screen

It's difficult to tell at this angle, but you'll notice the 3 linebackers are in a Tan Zero Tan alignment behind the 4-3 Over which we previously discussed. With Clemson in a boundary corner blitz, FSU is in a great call for a potential big gain. With a quick play-action fake, FSU wants to draw the linebackers towards the QB and free the line to block downfield.

However, Goodson and Ben Boulware read the line's initial pass block and begin to drop into coverage instead of crashing towards Cook. Then, both the offensive line and running back keys reveal the screen and both linebackers break towards Cook before the ball is even thrown. From there, the linemen and the play have no hope but Cook's elusiveness.

Clemson's linebackers played the screen beautifully; they read each key and stayed in position. From there the instinctive aggression and speed for which the position is known must take over. The best linebackers don't simply fly to where they think the ball will go; they read keys and fly to where they know it will go.