Could Pete Carroll cross old NFC West rivalry lines after being replaced by Seahawks?

The San Francisco 49ers are searching for a new defensive coordinator for the third time in three years. Niners head coach Kyle Shanahan and Steve Wilks struggled to get on the same page throughout the 2023 NFL season. Shanahan fired Wilks following the team's Super Bowl LVIII loss, which featured an overtime play call that left Shanahan visibly frustrated.

The Niners have built a reputation as one of the league's best defenses, but the unit allowed 149.3 rushing yards per game during the postseason. As they look to rebound from the abysmal performance, Shanahan and general manager John Lynch will need to make sure they hire the right coach to lead the unit during the 2024 NFL season.

One name that's been floated out into the ether? Bill Belichick, the legendary former head coach of the New England Patriots. While Belichick is the greatest coach in NFL history, the fit may not be right for either party. Instead, San Francisco's Play-by-Play Announcer Greg Papa suggested another renowned head coach to fill the void: former Seattle Seahawks head coach Pete Carroll.

Pete Carroll would be a perfect schematic fit for San Francisco 49ers defense

“I think [former Seattle Seahawks coach] Pete Carroll would be more of a natural fit,” Papa said during an appearance on the Rich Eisen Show. "Because with Belichick, he likes to vary his fronts — it would be a very different defense."

While there has been no shortage of animosity between Pete Carroll and the 49ers, the hiring would make perfect sense for San Francisco.

“What’s the best defense to run for Fred [Warner], Dre [Greenlaw], Nick [Bosa], Charvarius Ward, Deommodore Lenoir and Talanoa Hufanga?" Papa said. "That’s who you’re trying to serve. The defense that the 49ers are running since Kyle [Shanahan] has been the head coach is Seattle's defense. [Carroll’s] the guy who did it.”

Schematically, Wilks was never the right fit for San Francisco. Wilks, who served brief head coaching stints for the Arizona Cardinals and Carolina Panthers, established a reputation for implementing a versatile and aggressive scheme. A hallmark of WIlks' defensive philosophy is the emphasis on creating pressure on the quarterback from a variety of blitz packages, many of which include the linebackers rushing the passer. Shanahan wanted Wilks to run the same scheme that was already in place from San Francisco's former defensive coordinators, Robert Saleh and DeMeco Ryans.

"It was real tough losing DeMeco ... and Saleh the year before," Shanahan said. "We had committed to not just the system, but the players that had been in the system, from our [defensive] line or linebackers. They had played in it for such a long time. It was my goal to not have to change all of them, and bringing in Steve ... just ended up not being the right fit."

San Francisco 49ers' defensive scheme

Before becoming the head coach of the New York Jets, Saleh implemented a defensive scheme in San Francisco that drew inspiration from the Seattle Seahawks' famed "Legion of Boom" era. Carroll's Legion of Boom defense became known as one of the most formidable defensive systems in recent NFL history, and it fueled the Seahawks' dominance in the early to mid-2010s, highlighted by their Super Bowl XLVIII victory.

Formation

The defensive system primarily utilized a 4-3 base formation with an "Under" alignment. The formation features four defensive linemen and three linebackers, with the defensive line shifting towards the weak side of the offensive formation. This positioning allows the defense to leverage against both the run and the pass, with a focus on setting strong edges — something the 49ers struggled to do during the 2023 campaign.

Coverage

At the heart of the Seattle scheme is a Cover 3 zone coverage, where the secondary is divided into three deep zones that are typically covered by two perimeter cornerbacks and one middle-field safety. That leaves the linebackers and strong safety to cover intermediate zones and provide support for the run defense.

The defense employs a mix of zone coverage schemes with matching principles. That means that while the coverage begins with zone coverage, defenders have the flexibility to switch to man coverage based on the routes run by the opposing wide receivers. This hybrid approach allowed the defense to better adapt to the variety of passing concepts that would generally be used to attack the weaknesses of Cover 3.

The San Francisco 49ers established themselves as one of the league's premier defenses by building a defensive roster that fit the scheme. Former defensive coordinators Robert Saleh and DeMeco Ryans were both well-versed in the scheme, which is why the defense thrived under them. Wilks was an outsider without any familiarity with the scheme, and the 49ers seem to recognize that it was a misstep to hire him.

With Saleh and Ryans no longer being available, who could run the Seattle defense than Carroll himself?