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Film room: Defensive player review part 2 - Kwon Alexander’s breakout year comes to an end and what his replacement Dre Greenlaw brings to the defense

Kwon Alexander anchors a linebacker group with superior run defense, ability to create turnovers, and coverage ability to break up passes

San Francisco 49ers v Washington Redskins Photo by Rob Carr/Getty Images

The other half of the linebacking duo is Kwon Alexander, who was having a career season until he was sidelined and placed on the injured reserve list after tearing his left pectoral muscle in the week nine Thursday Night Football game. The 49ers originally signed the former Buccaneers linebacker Alexander in the offseason, making him a generously paid linebacker even after his season ending ACL injury in 2018.

One could easily make an argument the 49ers overpaid for a linebacker but the team was in between a rock and a hard place, lacking depth at the position after Warner, after letting Reuben Foster go for off-the-field-issues.

However, Alexander is a younger and more experienced linebacker than Foster was and was very athletic pre-ACL injury. In fact, he still is. The ACL injury has not limited him this season and he’s showcased some of the best results of his career. In many ways he was the linchpin for the defense prior to his season ending. What did he do well and not so well and what does his replacement Dre Greenlaw offer in his absence?

Kwon Alexander

Run defense

Alexander benefitted playing behind an elite defensive line this season, but that only allowed him to refine his skills and showcase why the 49ers picked him up.

Alexander struggled early on in run defense while with the Buccaneers, lacking the instincts to fill his run gap and recognize which linebacker flow to play. The first clip in the video is an example of this from Warner’s days with Buccaneers. The play is a toss crack to the left but Alexander’s first step is downhill (tight flow technique) and upon recognizing the toss (fast flow), it should be lateral , with the linebacker attempting to flow down the line and get out of the box to make a play.

The second and third clips above show Alexander reading and reacting better than he did early on and it’s paid off. Both plays are wide zone schemes away from Alexander. He’s responsible for the back side C-gap in both instances too. And both times, he flows laterally with the wide zone (fast flow) and compresses or squeezes his run fit in the C-gap and stopping the running back for a minimal gain.

Fast flow linebackers also have to be able to get out of the box and rally quickly to the ball carrier if the play hits to their side. Here, Alexander shows that sideline to sideline speed getting out of the box necessitates. Alexander reads his run cues, the pulling center, and immediately gets lateral to the edge. The center is tied up with defensive lineman Arik Armstead so Alexander gets outside, forces running back James Conner back in, but manages to finish with a tackle for a loss.

Creating turnovers

Alexander has one interception and one forced fumble on the season—both coming at crucial times. In Week 7, with Washington mounting a potential scoring drive, the defense got yet another spark from Alexander when he forced a fumble setting up a third quarter scoring drive.

In this particular game, neither team could run the ball effectively due to the weather. Knowing this, the defense put seven defenders in the box. Jullian Taylor and Ronald Blair wreck the right side of the offensive line; Taylor gets penetration and Blair spills Peterson back inside where Alexander awaits after beating his blocker. Sheldon Day grabs Peterson and Alexander comes in, swatting the ball out of Peterson’s grasp. Taylor managed to scoop it up quickly.

Against the Bengals in week two, Alexander recorded an interception when he intercepted a hurried pass from quarterback Andy Dalton as he [Dalton] was flushed from the pocket by Nick Bosa. Alexander’s interception was on a drive the Bengals needed to get points on. And shows

On a fire zone blitz, the 49ers are running a tackle-end exchange stunt to the right with Bosa looping inside behind defensive tackle Deforest Buckner, who drew two blockers when Bosa peeled off to loop around. Nickel defender K’Waun Williams came off the edge to occupy the running back which removed three blockers as Bosa loops through the A-gap.

Bosa’s gets a free run through Dalton’s throwing lane and forces Dalton from the pocket to his right to avoid the sack. As Dalton scrambles, he rushes a throw to his receiver, whom Alexander stuck with across the field with underneath leverage that Dalton doesn’t see. Dalton throws into the coverage and Alexander finishes with the interception.


In pass coverage, Alexander actually has the second highest coverage grade of anyone on the defense with an 81.7 (K’Waun Williams has the highest at 82.7). In addition to being able to effectively cover as seen in the interception above, he’s also skilled at reading the play and being in the right spot to get the pass break-up while not necessarily covering a receiver. His ability to drop back in zone coverage with little to no wasted movement allows him that extra jump needed to break up passes.

Against the Bengals, Alexander had three pass break-ups (one being the interception above), and another completion against him went for zero yards because of his ability to expertly read and react to the ball. Alexander reads the single receiver and squeezes him into the coverage in the clip above as he’s re-routed inside to Alexander’s weak hook zone. As soon as Dalton looks to his left, Alexander is already breaking to the receiver. He isn’t able to intercept it, but he makes a leaping attempt and bats it up and away.

In addition to being an excellent zone defender and decent in man coverage, he’s also one of the best at reading and reacting to screens and passes out of the backfield because he is able to understand certain offensive keys and see them as they develop.

In this clip from week two, he breaks on running back Gio Bernard out of the backfield as the ball is thrown. He stays square to the line of scrimmage and mirrors Bernard’s movement as he breaks on the pass. As soon as Bernard catches it, Alexander hits him square on and knocks the ball loose for an incomplete pass.

Recognizing the Bengals need of one yard on second down, Alexander lines up just inside of tight end Tyler Eiffert and off the ball. The play is a tight end pop pass where Effiert “pops” off the line of scrimmage quickly expecting a pass. As Dalton goes to throw, Alexander is in great position to read the play as he didn’t get sucked in by the play action. He breaks on Eiffert in the open field, stays square, and finishes with a tackle for no gain.

Dre Greenlaw

When I started this article, Kwon Alexander had not yet been lost for the season with a torn pectoralis muscle. In the Week 9 Thursday Night Football game, Alexander suffered the injury and was placed on season ending IR.

Rather than just make this article about him, I decided to put some clips in and show what the defense gets with Dre Greenlaw, who will replace Alexander at the WILL linebacker position and become the every down linebacker next to Fred Warner.

Greenlaw is a rookie out of the University of Arkansas drafted in the fifth round of the 2019 NFL Draft. He played most of OTAs with the first team defense due to Warner and Alexander rehabbing injuries in the offseason.

By camp, he had made a name for himself, and continued taking first team reps when Warner and Alexander returned at the start of training camp. He gained more attention for thundering hit he put on fullback Kyle Juszczyk in what was supposed to be a non-contact padded practice. Outside of football, he’s also tremendous given a story that floated around after his drafting.

Do the 49ers gain or miss anything with Greenlaw in the lineup in Alexander’s absence? Well, pass coverage comes to mind. Alexander’s 81.3 coverage grade per Pro Football Focus ranked him tied for 7th in the league. Greenlaw’s coverage grade of 61.2 ranks him 58th. He’s surrendered eight catches on nine targets but only 45 total receiving yards, 21 of which came late in the game against Carolina when they were throwing further downfield to salvage an already embarrassing loss.

Pass defense

In pass coverage, while there aren’t any snaps of him covering anyone man to man (unless I missed it?), he does show good zone awareness to “ROBOT” the deep crossing routes teams like to run out of trips or doubles. ROBOT technique for a linebacker means they are to “rob and get underneath” any deep crosser. It’s much easier than running with a speedier more athletic receiver. If a linebacker can come drop off underneath any deep route in his zone, it’s much more advantageous to do so than asking another to run with him.

Against Tampa Bay in Week 1, with the Buccaneers in the red zone needing a much needed score, Greenlaw denied them a big-play opportunity when he located the dig from the slot early and sinks underneath the deep cross from the far hash. Winston is initially looking for the deep crosser but sees that it’s taken away by Greenlaw and by that point he has to scramble.

A few plays later, the defense would get a fourth down stop after the Buccaneers had to work to get inside the five. Had Greenlaw not been there on the play above, they likely would’ve scored.

Greenlaw also has an ability to sniff out screens and played a small part in the pick-six the 49ers recorded in week one versus the Buccaneers when he disrupted the downfield blocking of the Buccaneers offensive line and not giving the running back any room, forcing quarterback Jameis Winston into an errant throw.

Sideline to sideline

He also has decent ability to run sideline to sideline to make tackles limit the opposing offenses to small gains.

Other than that, there isn’t much to evaluate in the passing game other than that he shows off good closing speed to make the tackle and not give up a big gain but lacks instincts to recognize and understand route concepts that he could face. That’s not to say he doesn’t have the instincts but he just hasn’t been in a position where he can develop them.

Run defense

The defense may get a boost against the run from Greenlaw though, who boasts a better run defense grade and tackling grade than Alexander. Against the run, Alexander’s biggest weakness was missed tackles. Though there is nearly a 50 point grade differential between the two on run defense, I am not too worried about a team beating the 49ers with their ground game alone.

The main difference between Alexander and Greenlaw is the ability to read and react to the various run schemes of different teams. Whereas Alexander reads and reacts almost instantaneously, Greenlaw is still developing that skill and playing in a system that utilizes the instincts of the linebackers to greater effect than anything else. He has the athletic ability to make plays, but he needs time reading the flow of the offense before that really kicks in.

On this play against the Cardinals late in the third quarter, Greenlaw’s read is “full flow” against a gap scheme power run. As the full flow against the pulling blocker, Greenlaw should work to compress his run fit rather than expand and attack the inside the shoulder of the pulling guard closer to the line of scrimmage, not two or three yards beyond it. Instead, he takes the blocker square on and widens his fit, allowing the running back to get up in the hole for a gain of eight.

He has shown flashes of being able to read and react quickly though, so it seems that this is one area that he will eventually develop with time.

Against Tampa Bay in week one here, he’s lined up as the WILL and shows an ability to keep himself clean and not get washed out of the play on the weak side, instead scraping over the top into the hole to clean up the play.

Here against the Steelers, he gets downhill immediately after reading the inside zone blocking and meets the running back at the point of attack for the stop.


Alexander rounds out a linebacker group playing at an elite level in the way they read and react to plays in both the pass and run and his instincts and aggressive approach to the defense will be sorely missed. Greenlaw should be a solid replacement but he still lacks the instincts to be able to pick up where Alexander left off. Playing behind this defensive line should allow Greenlaw to refine his skill set as offensive players reach the second level.In the next part of the player breakdowns on defense, we’ll look at the secondary players anchored by veteran Richard Sherman.