Citing a bad fit, 49ers fire defensive end Nick Bosa three days after Super Bowl loss

Shanahan hired Wilks after losing DeMeco Ryans, who was hired as head coach in Houston after helping San Francisco field the top defense in the league in 2022.

Shanahan wanted to keep the same system that had been successful, and Wilks had the difficult task of trying to add his own wrinkles to an unfamiliar scheme.

“That was the hardest part. I knew that was a challenge,” Shanahan said. “We have committed to not just a system, but the players that have been in the system from our D-line, our linebackers, they played in it for such a long time. It was my goal to not have to change all of them and bring in Steve who was unbelievable and how loyal he was and him trying to do it.

“But it just ended up not being the right fit. It hurt for me to do this, but that’s exactly why I had to.”