They've done it with one of the youngest secondaries in the league -- none of the current starters is older than 25 -- and with a collection of players who were considered near the bottom of the scrap heap, mainly fifth- and sixth-rounders deemed either too big, too small or just not the right fit.
Carroll, who got his start coaching defensive backs nearly four decades ago, took an unconventional approach. He put big, athletic bodies in spots that were normally occupied by the small and swift.
He built a secondary with a chip on its shoulder the size of Mount Rainier.
"These guys come from diverse backgrounds," Carroll said. "They come from L.A. to Texas to the hills of Virginia. I mean, they're as spread out as you can get. But I think it's the cause that brings them together. They have joined in to be great. And they're going to do whatever it takes, and part of that is helping each other be at their best."
There is just one true requirement to play in the Seahawks secondary, according to Carroll. A guy has to know how to catch the ball. Confidence is paramount, too, because Carroll oozes it.
The day before the regular-season finale against the St. Louis Rams last month -- a game that would clinch the Seahawks' NFC West title -- Carroll brought in Bill Russell to speak to the team.
"He was like, the night before the playoffs, everyone would ask him, 'Are you nervous?'" cornerback Byron Maxwell said, recalling the speech from Russell. "And he's like, 'No. I'm not playing Bill Russell and the Celtics.' So it's kind of like that mindset. They've got to deal with us.
"It's not cocky. It's confidence."
Each Legion of Boom member has a role. Chancellor is the enforcer. He is built like a linebacker. His hits are so ferocious that, according to a Twitter feed from former Arizona Cardinals safety Hamza Abdullah that made the rounds locally, Chancellor once leveled a tight end so hard that Abdullah saw the kid's soul "leave Qwest Field right on that 35 yard line."
Sherman is the brains behind the operation. He's also long and athletic and can catch nearly anything, leading the NFL with eight interceptions in 2013. Earl Thomas is probably the ringleader, the one who's the only first-round draft pick of the bunch (2010), the one who's always in the middle of the pile, who treats every day as if it's his last game. Thomas is the smallest player in the secondary at 5-foot-10. But the free safety's mere presence prevents big plays. "Think about how many times over the last couple of years you've seen a post route," Carroll said, "which is one of the most common routes in football, thrown at our defense for a big play. It doesn't happen very often. I can barely remember any of them."
And then there's Maxwell, a quiet cornerback who was a sixth-round pick out of Clemson in 2011. Maxwell has had four interceptions in the past four games.
Sherman pauses when asked about Maxwell's role. "I'm trying to think of the perfect analogy," he said. "He's the new kid on the block."
Maxwell has taken the place of Walter Thurmond, who was suspended four games for violating the league's substance-abuse policy.