The decision to replace Kris Richard with Ken Norton Jr., which became official Tuesday, is the most surprising of all the moves head coach Pete Carroll has made over the past week in overhauling his Seattle Seahawks coaching staff.

The question isn't just why he'd fire Richard as defensive coordinator after a trying season in which Seattle lost three Pro Bowlers on that side of the ball. It's also why he'd bring back Norton after passing him over three times for that position dating to 2010, Carroll's first season in Seattle.

Carroll could have made Norton his defensive coordinator that year but instead retained Gus Bradley, a holdover from Jim Mora's only season as Seattle's coach. In 2013, Carroll brought back Dan Quinn when Bradley left for the Jacksonville Jaguars, and two years later he promoted Richard when the Atlanta Falcons hired Quinn following Seattle's second straight Super Bowl appearance. That's when Norton left to become the Oakland Raiders' defensive coordinator after spending five seasons as Seattle's linebackers coach, the same job he held at USC under Carroll.

No credible case can be made based solely on their résumés as coordinators that Norton is a better man for the job than Richard. Seattle ranked second and fifth in total defense in Richard's first two seasons, then 11th in 2017. Oakland's defense was 22nd and 26th in Norton's two full seasons there -- albeit with less talent and a different scheme than Seattle's -- and it wasn't faring any better when he was fired in November.

In the absence of an explanation from Carroll, we can take only educated guesses as to why he's essentially redoing his 2015 decision to promote Richard over Norton. Clearly, though, it's about much more than bottom-line results.

At the heart of it could be Carroll's desire to regain control of his defense in a way that could have been -- or perhaps was already being -- met with resistance from Richard. That would explain rumblings of tension between the two this past season.

To be clear, this is very much Carroll's defense, one shaped by his time with Monte Kiffin in the late 1970s and one he's run in Seattle without much change regardless of which coordinator he's had calling it. That could have made it a tricky proposition for Carroll to step outside of his own coaching tree to find the next one. In that regard, it made plenty of sense to turn back to a former assistant with a deep understanding of his defense and how he wants it operated.

Whether he was Carroll's first choice -- Bradley, anyone? -- Norton fits that bill. He spent six seasons under Carroll at USC and five more in Seattle.

Norton, 51, is known less as a master tactician and more as a master motivator, a coach with a strong ability to relate to players who still commands respect. He's every bit the enforcer that you'd expect from someone who played linebacker for 13 seasons in the NFL and whose father, Ken Norton Sr., was a heavyweight boxing champion who once broke Muhammad Ali's jaw.

That surely appealed to Carroll in light of notable instances of players -- mostly on the defense -- either breaking or stretching the limits of his No. 1 rule: protect the team. There was the sideline outbursts from Richard Sherman in 2016 and the drama that followed. More recently, Doug Baldwin shoved offensive-line coach Tom Cable this past season during another heated moment on the sideline. Bobby Wagner and Earl Thomas had their bizarre postgame tiff a week before Thomas' "come get me" remark to Dallas Cowboys coach Jason Garrett.

Those aren't the types of things that would seem to fly on Norton's watch.

That's not at all to suggest Richard lacked respect from his players. In fact, it's believed that endorsements from Sherman, Thomas and Kam Chancellor helped tip the scales in Richard's favor when Seattle promoted him from defensive backs coach to defensive coordinator in 2015. Richard played a hands-on role in grooming those players into stars.

But the defense that produced historic results from 2012 to 2015 -- leading the league in scoring in each of those seasons -- might be undergoing a shift in leadership from its secondary to its linebacker corps. While the Legion of Boom was at its peak when Richard became the defensive coordinator, all three of its remaining charter members face varying degrees of uncertainty with their futures. A neck injury could prevent Chancellor from playing again, while Sherman and Thomas are signed only through 2018. Sherman will be 30 years old next season and coming off a ruptured Achilles, and Thomas has expressed skepticism about the team extending him.

Meanwhile, Wagner is in seemingly as secure of a position as anyone on Seattle's defense. He was the team's defensive MVP last season and earned first-team All-Pro honors for the third time in his career. He's signed through 2019 and will be only 28 next season.

Wagner and fellow linebacker K.J. Wright, both huge fans of Norton, reacted positively on social media to the news of his hiring.

That isn't a flashy move, nor is it one that makes complete sense on the surface. But in Norton the Seahawks might have the best of several worlds -- a well-liked coach who can maintain order and command respect from his players but also one who doesn't mind deferring to Carroll over how his defense is run.