How 49ers can mitigate loss of linebacker Kwon Alexander

With San Francisco 49ers linebacker Kwon Alexander expected to miss the remainder of the 2019 season with a torn pectoral, Niner Noise explains how to lessen the blow.

In a season where everything seemed to line up for the still-undefeated San Francisco 49ers, they’ve been constantly afflicted with injuries. Wide receivers Trent Taylor and Jalen Hurd both seem unlikely to return this season, and other cogs like the bookend tackles, missed significant time.

Now, linebacker Kwon Alexander joined the growing list. He tore a pectoral muscle during the Niners’ 28-25 Thursday Night Football win over the Arizona Cardinals, ending his season.

Alexander’s impact on the defense went far beyond the counting stats, seen here by Pro Football Focus:

San Francisco as a whole has struggled against the run, yet has played well against the pass. That’s on par with Alexander’s performance. But beyond that, he brought the Niners a swagger they had lost in the post-Jim Harbaugh years.

With Alexander now on the bench, that swagger is lost a little. That’s not something the Niners will be able to replace.

However, they have no choice but to try and replace his performance.

The most likely replacement would be rookie linebacker Dre Greenlaw, who had been playing strong-side linebacker (SAM) but would move over to weak-side linebacker (WILL). Either Mark Nzeocha or Elijah Lee, who is currently on the practice squad, would fill in at SAM.

In base packages against the run, that wouldn’t cause too much concern. Greenlaw’s struggles don’t come from not reacting; they come from over-reacting to plays. The Niners as a team have struggled there, so it’s not like the defense would be losing something. Of course, the young rookie would have to temper his pursuit, but the drop-off is manageable.

In pass coverage, the issues compound. Greenlaw simply doesn’t have the processing ability Alexander does, which is a result of experience. In preseason, Greenlaw was baited on play action, often over-reacting to what was in front of him. As the graphic above detailed, Alexander had been incredible in coverage.

The solution here isn’t nearly as simple. Greenlaw cannot match Alexander’s production; assuming so is illogical.

There is, however, another option to mitigate the loss of Alexander’s coverage.

A part of that laundry list of injuries was cornerback Ahkello Witherspoon. His foot injury thrust Emmanuel Moseley to the spotlight where, until his last game until against the Cardinals, played lights out. Now that Witherspoon is scheduled to return, the Niners will move Moseley to the bench.

One key aspect of Moseley’s game, at least in the preseason, was how he could play both slot corner and outside. In this thread by former NFL cornerback Eric Crocker, he breaks down Moseley’s abilities in both positions.

No replacement linebacker on the 49ers could replace the job Alexander did in nickel formations, but a cornerback certainly could, especially one with the abilities of Moseley. The 49ers would essentially shift to a dime (six defensive backs) defense instead of a nickel (five defensive backs) defense in passing situations. Moseley would replace the WILL, just as cornerback K’waun Williams replaces the SAM in nickel formations.

Now this would put the run defense in a precarious position, but in certain circumstances that would call for a passing attack counter or with schematic covers to help the situation, it could be highly effective.

The other option would be to put a safety at linebacker, with Marcell Harris the primary choice. But the run-game benefit in the nickel set would be much less than the coverage loss. Another option would be to shift Jimmie Ward to strong safety, put Tarvarius Moore at free safety, and bring Jaquiski Tartt down in the box in another dime look. But that would put both Tartt and Ward, who have been great, in new positions.

Alexander was playing well this season, but the 49ers defense has ways to mitigate the loss. How they respond to yet another setback will be critical for the second half, and hopefully, the second season.