49ers’ struggling defense looks to slow down Chiefs in Super Bowl

The 49ers were one of the favorites to reach the Super Bowl in large part because of their star-studded defense.

They made it here in spite of that unit.

Even with the most expensive defensive line in the NFL and All-Pro talent at all three levels, San Francisco struggled to slow down its two postseason opponents.

The surprisingly leaky defense will be under the microscope Sunday when the 49ers are tasked with containing quarterback Patrick Mahomes and the Kansas City Chiefs in Super Bowl 58 at Allegiant Stadium.

“It’s not so much a chip (on our shoulder) to prove other people wrong,” 49ers defensive coordinator Steve Wilks said Thursday. “It’s really that chip to get back to where we know we’re capable of playing. We’ve been a great defense around here for a long time. We play with a certain passion and physicality, and that’s what those guys are looking forward to doing on Sunday.”

Led by defensive end Nick Bosa and linebacker Fred Warner, the 49ers gave up the third-fewest points in the NFL and were eighth in yards allowed per game. San Francisco was particularly strong against the run, as only the Bears and Lions allowed fewer yards on the ground.

But after holding 10 of its first 13 opponents under 100 yards rushing, the 49ers started to show cracks late in the regular season, particularly after run-stuffing defensive lineman Arik Armstead was sidelined with knee and foot injuries for the final five games.

San Francisco was gashed for 234 yards on the ground in a 45-29 win over the Cardinals in Week 15 and also gave up more than 100 yards rushing in late-season losses to the Ravens and Rams.

The difficulties against the run continued in the playoffs, even with Armstead back, as the 49ers allowed 136 yards rushing to the Packers in a 24-21 win during the divisional round. Lions running backs David Montgomery and Jahmyr Gibbs battered the 49ers defense in the NFC championship game, and Detroit finished with 182 yards on the ground as the 49ers rallied for a 34-31 win.

The 49ers allowed minus-67 rushing yards over expected during the regular season, per Next Gen Stats, which ranked eighth in the league. In two playoff games, they allowed plus-79 RYOE, the worst in the NFL.

The lack of effort in particular on two touchdown plays against the Lions was addressed by the coaching staff and general manager John Lynch. Wilks last week called the performance “unacceptable” and “embarrassing.”

“It was bittersweet, both those games, because obviously you’re so happy and excited you won the game and you’re able to advance … but also knowing that’s not our standard for defensive play ever since I’ve been here,” Warner said. “That’s something that’s been a point of emphasis.

“I love our mindset right now. I think guys are going about the work the exact right way this week. That has been handled in-house, and I think we’ll be ready to go and fully prepared for Sunday.”

The 49ers’ defense went through an uncomfortable film session following the win over the Lions and spent over a week looking itself in the mirror. They know a repeat performance won’t cut it Sunday against the defending champion Chiefs.

“I think we’ve played good in the second halves (during the playoffs),” Bosa said. “But we want to put together a whole game, for sure.”

Contact David Schoen at dschoen@reviewjournal.com or 702-387-5203. Follow @DavidSchoenLVRJ on X.