The 49ers have a 305-pound hole to fill. Here’s the key to replacing Javon Hargrave

Former San Francisco 49ers edge rusher Arden Key, who was with the team in 2021, coined an adage that’s lived on in the team’s defensive line room ever since.

“Stop the run, and we can have some fun.”

The premise was simple. Discouraging opponents from running the ball would force them to throw excessively, thereby creating opportunities for pass rushers to execute their specialty: hunting quarterbacks. 

That 2021 season saw the 49ers’ pass rush roar to life down the stretch, fueled in large part by a run defense that ranked No. 1 over the back half of the season. The team recovered from a 3-5 start to reach the NFC Championship Game. Key’s proverb became etched in the 49ers’ lexicon.

But now, three seasons later, the 49ers are struggling to live up to it.

Their 2022 defense finished ranked No. 1 overall, with the run defense at No. 2 based on expected points added (EPA) per play. But the 2023 unit tumbled to No. 10 overall — and No. 26 against the run. Over three games to begin 2024, the 49ers rank No. 24 defensively — and No. 28 against the run.

And now there’s another complication. Defensive tackle Javon Hargrave tore his triceps muscle in last Sunday’s loss to the Los Angeles Rams, so he’s likely out for the season.

The 49ers are at a pivotal crossroads entering their Week 4 game against the Patriots. New England’s top running backs, Rhamondre Stevenson and Antonio Gibson, weigh 227 and 228 pounds, respectively. They’re two of the most bruising runners in a league that’s now mostly filled with relatively smaller backs. The 49ers’ ability to adapt against the run will be put to an immediate, hard-nosed test.

Defensive end Nick Bosa said the 49ers are busy making schematic adjustments after allowing 244 rushing yards over the past two weeks. Coach Kyle Shanahan said that the 49ers might implement some more varied defensive fronts. They’ve employed five-linemen fronts on select occasions to slow the run in recent seasons. But Bosa emphasized that the biggest key might be establishing better cohesion between the line and the back seven, since the 49ers’ aggressive “Wide 9” alignment — which is geared toward pass-rushing success — creates so much natural space to fill against the run.

The 49ers made a big splash in adding the 305-pound Hargrave at $21 million annually prior to the 2023 season. They were desperate to rediscover an interior rush following a 2022 campaign where the team’s defensive tackles managed only four combined sacks.

Hargrave indeed helped shore up the pass rush — he led the team with five pressures against the Rams — but the run defense continued to sputter even when he was available.

So while it’s unrealistic to believe that the 49ers can find a plug-and-play pass-rushing replacement for Hargrave in the middle of this season, perhaps they’ll be able to replace his snaps with a more effective run defender. And this, at least in theory, could boost the entire defense — including the pass rush.

A natural option for a greater role is 320-pound defensive tackle Jordan Elliott, who joined the 49ers in free agency this past offseason and has averaged about 20 snaps per game so far.

“I think he fits the scheme really well,” Bosa said of Elliott. “He played in Cleveland on the No. 1 defense last year, so he got a feel of what it’s like to play in this type of scheme. He’s comfortable and he’s massive, which is a little different for our interior guys. But it’s always good when you can be big and explosive like he is.”

The 49ers previously enjoyed that type of skillset from defensive tackle D.J. Jones. He anchored the run defense to its No. 2 overall finish in 2021 before signing with the Denver Broncos in free agency. Perhaps it’s no coincidence that the 49ers’ run defense tumbled about a year later.

Speaking during training camp last month, 49ers defensive line coach Kris Kocurek seemed particularly excited about Elliott.

“We haven’t that type of size since D.J. left in 2021,” Kocurek said. “We haven’t had that 320-pound frame, especially down in there in the A-gap since D.J. left. D.J. was a presence, and we feel Jordan has the ability to be that type of presence.

“If you’re going to be a big man, you’ve still got to generate the explosion that the system asks for. It’s like a puzzle up front. You can’t have three guys attacking and one guy just sitting there, not creating a new line of scrimmage. It works in waves.”

And the 49ers hope to start coming in more effective waves this Sunday, when New England is certain to test them with the ground and pound. Defensive lineman Yetur Gross-Matos, another potentially key replacement for Hargrave thanks to his ability to slide inside to tackle from end, emphasized that the 49ers must embrace a proper mentality to stop the run.

“In our scheme, we get off the ball, we attack — we’re not reading, we’re just going,” Gross-Matos said. “So we have to go out there with the right mindset: Run through somebody.”

Stop the run and have some fun.

“It’s the key this week, for sure,” Bosa said.

• The 49ers listed Brock Purdy with back soreness earlier this week, but the quarterback was full-go at practice Wednesday. An MRI Monday came back negative on Purdy, who’s now topping the NFL charts in some advanced efficiency metrics:

• Receiver Deebo Samuel Sr. did not practice again. He’s expected to miss at least one more game with his calf strain. Linebacker Dee Winters, who hurt his ankle against the Rams, also didn’t practice Monday. Tight end George Kittle, who’s dealing with a hamstring injury, was back out at practice in a limited capacity. Left tackle Trent Williams missed Wednesday’s practice with an illness.

• A day after releasing veteran safety Tracy Walker III from their practice squad, the 49ers signed defensive tackle Shakel Brown to fill that open spot. With safety Talanoa Hufanga back in the lineup, the team no longer needed the insurance policy Walker brought to the position.

Brown had initially been with the 49ers in the offseason after a tryout led to the team offering him a contract. He’s back as interior depth for a team that’s now working to weather the loss of Hargrave. Fellow practice squad defensive tackles T.Y. McGill and rookie Evan Anderson may be vying with Brown to replace Hargrave’s spot on the 53-man roster.

• Receiver Ronnie Bell had a rotten game against the Rams, dropping numerous passes including a late deep ball from Purdy that probably would’ve given the 49ers a win. Bell said that Purdy himself has helped him overcome Sunday’s disappointment.

“The best thing for me in the last couple days was Purdy coming and talking to me,” Bell said at his locker. “He really helped lift my spirits, man. It helps a lot to have guys having your back like that.”