Glossary Entry: Key and Diagnose

“Key and Diagnose” is one of the most vital abilities defensive players have. Depending on the position, there are certain “keys” that defenders must read to “diagnose” what the offense is doing, so they can react appropriately. Scouts use the term “key and diagnose” (K&D) when evaluating a defender’s ability to read his initial key and then diagnose the offensive play/concept efficiently.

Defensive coaches talk about “playing fast,” but playing fast is not merely a function of foot speed. To play fast, a defender must not only be able to get from point A to point B quickly, but also to determine what the proper point B is. A player with top-tier key and diagnose (K&D) can play much faster than his timed foot speed, often faster than superior athletes with poorer K&D. Play speed is a function of understanding your keys and assignment and allowing your athletic ability to shine because you can anticipate or react quickly, rather than being a step behind the play.

When a linebacker makes a tackle in the backfield, it is often a function of using his K&D skills to read the footwork or initial movement of the offensive line and processing that information to diagnose their intention so he can  react accordingly. Interior defensive linemen that are able to decipher pulling guards and get themselves in position to “spill” or “wrong-arm” a puller can take away the inside gap, force a runner to alter his track, and bounce it outside.

These are a couple of the examples we will take a look at in order to highlight what top-level K&D skills look like in the NFL.

First, we go to Indianapolis as their defense faces off against Carolina’s offense. The Panthers come out in 11 personnel and call a run-pass option (RPO) with a frontside deuce block and tight end Greg Olson (#88)slicing across the formation from the backfield as a lead-blocker.

Inside linebacker Jerrell Freeman (#50) makes a decisive read off of the deuce block through to the mesh point, inserting downhill off of the left tackle’s backside to fill the C gap. He initially takes too wide of a track to the outside to account for the possibility that Olson would receive the handoff, but quickly gathers himself and comes to balance in space to get square to the line of scrimmage once he realizes quarterback Cam Newton (#1) put the ball in running back Jonathan Stewart’s (#28) chest.

Freeman transitions back inside with a “wrong arm” technique to defeat Olson’s attempted block, plants his inside foot in the hole with the runner squared up, and unlocks his hips into contact for a strong wrap-up tackle.

This is an excellent example of a linebacker processing multiple reads with very little hesitation, coming to balance in space, staying square and using refined technique to defeat a block in order to put himself in position to make a tackle in the hole:


Next, we go to Pittsburgh as the Steelers take on the Cincinnati Bengals. The Steelers defense runs a series of gap exchanges with their front as linebacker Ryan Shazier (#50) scrapes over the top following the backside guard pulling on a power run concept.

Once Shazier gets to his spot he quickly comes to balance in space, settling in behind linebacker Jarvis Jones’ (#95) spill on the fullback, patiently waiting for the running back to make his next move. He does an outstanding job of transferring his weight and exploding outside as the runner bounces, targeting his inside hip for the takedown.

Shazier covered a lot of ground prior while traveling with the puller, settled and diagnosed what was in front of him, then finished the play for a tackle for loss:


Lastly, we go to the San Francisco 49ers vs. the Minnesota Vikings with defensive lineman DeForest Buckner (#99) highlighted for his ability to K&D a trap block.

At the snap, Buckner is in a 4i-alignment on the inside half of the left tackle. He is left unblocked by the tackle and left guard. He quickly realizes this and settles, working his eyes inside to look for a trap block. Buckner could have easily penetrated upfield for another step or two, but instead diagnosed what the linemen in front of him were doing, using that as a tell for what was coming next.

Once he reads the backside guard pulling to trap him, he seamlessly drops his inside shoulder with excellent pad level to “wrong arm” the blocker while keeping his outside arm free. This allows him to take on and stymie the block while putting himself in position to make the tackle in the hole:

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