After the San Francisco 49ers lost a low-scoring game to the Los Angeles Rams, defensive end Nick Bosa saw some hope for the team’s defense.

In the first 14 games under coordinator Nick Sorensen, the defense had been inconsistent. But in the game on December 12, where they limited the Rams to just 12 points and 4.6 yards per play, Bosa felt encouraged about the direction the defense was heading.

Bosa was so positive about the defensive progress that he suggested the defense, including Sorensen, should stay the same for 2025. He even said, “we have the right people in terms of coaches and players.”

However, after the 49ers defense allowed 38.7 points and 404.3 yards per game, with no takeaways in the final three weeks, Bosa changed his tune when asked about Sorensen.

“I think he’s a good coach,” Bosa said. “But it’s not my decision.”

The decision to move on from Sorensen was left up to coach Kyle Shanahan, who had supported Sorensen throughout the season. However, after the defensive struggles in the final weeks, Shanahan decided it was time to part ways with Sorensen.

Here is how the defense’s performance under Sorensen in 2024 compared to the previous year under Steve Wilks:

2023 (Wilks) 2024 (Sorensen)
PPG allowed 17.5 (3rd in NFL) 25.6 (29th)
Defensive efficiency 61.6 (9th) 47.32 (20th)
Defensive EPA 41.48 (9th) -57.71 (27th)
QBR allowed 51.1 (9th) 58.5 (26th)
Yards/rush 4.1 (14th) 4.4 (17th)
Yards/play 5.0 (7th) 5.2 (7th)
Yards/game 303.9 (8th) 317.4 (8th)
Red zone efficiency 54.5% (16th) 68.4% (31st)
Third down conversions 40.9% (24th) 43.1% (24th)
Takeaways 28 (T-5th) 17 (T-20th)

Now, the team is looking for its fourth defensive coordinator in as many years. Of the past three, only DeMeco Ryans stayed for more than one season before becoming the head coach of the Houston Texans. Steve Wilks lasted just one season after the 49ers made the Super Bowl last year. Unlike Wilks, Shanahan hopes to keep Sorensen in a different role.

According to Shanahan, the decision to move on from Sorensen was influenced by both the defense’s 2024 performance and the available options. Unlike the past two years, when the 49ers made deep playoff runs and many top coordinator candidates were already hired elsewhere, the 49ers now have the chance to hire anyone they want.

“It was a real tough decision,” Shanahan said. “I love Nick as a person and I love him as a coach… But just where we’re at, really as a team, where I think we need to go. There are a lot of big decisions ahead for us. And as hard as it is for me to come to this conclusion, I feel there are some options out there that can end up being a better option in the situation that we’re in for our team.”

The fact that many candidates now have experience as defensive coordinators is appealing to Shanahan. He had chosen Sorensen because of his familiarity with the 4-3 scheme Shanahan prefers, but Sorensen had never been a defensive coordinator before.

One of the top candidates this year is Robert Saleh, who was the 49ers’ defensive coordinator from 2017-2020 before becoming the New York Jets head coach.

Saleh runs Shanahan’s preferred scheme, knows the key defensive players still on the roster, and has shown he can adjust the defense when needed due to injuries or other factors. Saleh interviewed for the job on Thursday, and a reunion between him and the 49ers is possible, if not likely.

The challenge with hiring Saleh is that he has head coaching interviews with the Jacksonville Jaguars and Las Vegas Raiders. If he becomes a leading candidate for one of those positions and the hiring process takes longer, it may be difficult for Shanahan and the 49ers to wait while other coaches are hired.

Another potential candidate is Jeff Ulbrich, who replaced Saleh as the Jets’ interim coach. Ulbrich, a San Jose native who played linebacker for the 49ers for 10 years, also runs the scheme Shanahan prefers. Ulbrich could become available depending on how things unfold in New York.

While Robert Saleh and Jeff Ulbrich are seen as top candidates, another name to watch is Dennis Allen, the former head coach of the New Orleans Saints. Allen has a lot of experience, having worked for eight years as a defensive coordinator with the Denver Broncos and New Orleans Saints.

He also spent almost six seasons as a head coach with the Saints and Raiders, and another year as the senior defensive assistant with the Saints.

Shanahan has always respected Allen, especially after the challenges Allen’s defense posed to Shanahan’s offense in a November 2022 game, where the 49ers scored just 13 points and averaged 4.7 yards per play against Allen’s Saints.

Although the Saints fired Allen during the 2024 season, he still has a year left on his contract. This means Allen could take the year off while still being paid if he chooses to. However, during an appearance on the “Unbreakable with Jay Glazer” podcast, Allen mentioned that he would likely look for other coaching opportunities.

He has been linked to the Indianapolis Colts’ defensive coordinator opening and could also be a candidate to join Ben Johnson’s coaching staff if Johnson gets a head coaching job elsewhere. This means the 49ers would have competition for Allen if they decide to pursue him.

Brandon Staley, who joined the 49ers as assistant head coach last offseason, is the only known candidate from within the team. Shanahan has said he plans to interview Staley again.

Other well-known candidates who could attract interest include former Indianapolis Colts coordinator Gus Bradley, former Cincinnati Bengals defensive coordinator Lou Anarumo, and Raiders defensive coordinator Patrick Graham (if he becomes available). Detroit Lions defensive passing game coordinator Deshea Townsend has also already interviewed.

“I think having the experience of going through this before, building things before, I think is definitely a bonus for me,” Shanahan said. “It helps me with some stuff… But again, you don’t want to put just any handcuffs on your decision. You’re going to always try to figure out the best one.

So, you’ve got ideas going into that but just being so early I’m going to have an opportunity to talk to a number of guys too, so we’ll see what that leads us to.”

One of the main questions in this search is whether Shanahan will stick with the defensive principles he has favored since becoming head coach in 2017. These principles include heavy use of zone coverage, rarely blitzing, and primarily using four-man fronts.

Since 2017, the 49ers have played zone coverage on 61.2% of opponent dropbacks, which is the highest rate in the league. They have also blitzed the fifth-lowest rate in the NFL (22.4%).

Although Shanahan has stuck with this scheme in past coordinator searches, he is more open to other ideas this time, which could give someone like Staley, who was trained by Vic Fangio and prefers more varied defensive looks, a chance to be considered for the job.

The struggles of the 49ers’ defense in 2024 showed Shanahan that the next coordinator needs to be able to adjust when faced with injuries or other issues.

“I love the scheme that we’ve had here,” Shanahan said. “I think it’s one of the hardest things to go to when you’ve got the right guys in the right spots.

I’m not saying you’ve got to change schemes, but you have to have the ability, the history and the knowledge of how to change some stuff up when you’re in some certain situations. And I think that we do need that more going forward.”