It is possible, maybe even probable, that the Seattle Seahawks' famed Legion of Boom secondary has played its final defensive snap together.

When viewers tune in to see the Seahawks and Atlanta Falcons on Monday Night Football, they will see only free safety Earl Thomas remaining from the secondary that has driven much of Seattle's historic success on defense during the Pete Carroll era.

Left cornerback Richard Sherman is beginning an arduous rehab from a torn Achilles tendon and will be 30 years old heading into the final year of his contract. Strong safety Kam Chancellor, who will turn 30 four days after Sherman does, has missed 11 of the Seahawks' past 50 games and could miss the final seven this season if his neck injury is as ominous as reports suggest.

With age, injuries and contractual dynamics imperiling one of the NFL's most iconic defensive backfields, it's prime time to assess past, present and future.

The utter improbability of it all

The Seahawks will be without Kam Chancellor, left, and Richard Sherman when they take on the Atlanta Falcons in Week 11. Have we already seen their last game together as Seattle teammates? Mark LoMoglio/Icon Sportswire

For as excited as Carroll and general manager John Schneider were about selecting Thomas in the first round of the 2010 draft -- they feared Philly would snag him one spot earlier -- part of the public conversation centered on whether another safety, Taylor Mays, might have been a better choice given his ties to Carroll at USC. (Yes, that was an actual conversation at the time.)

Chancellor was so unusually large for a safety that some thought he was a man without a position in a traditional defense. He was the same height and weight as Aaron Rouse, a safety Green Bay had selected in 2007, when Schneider was with the Packers. There was discussion in the Seahawks' draft room over whether Chancellor would struggle in space the way Rouse and other longer-levered safeties had struggled, even though Chancellor had shown enough body control to ultimately temper those concerns.

"I thought Kam was going to be a linebacker," said former Washington Redskins and San Francisco 49ers general manager Scot McCloughan, who was a Seahawks personnel evaluator from 2000 to 2004 and 2010 to 2013. "He was that big, but Johnny [Schneider] and Pete saw it. The thing that is cool about it is, it's not just the player part, but the person you are getting. Kam didn't test off the charts, he wasn't a pretty guy, wasn't the most athletic, but just a football player through and through, which ended up being the case with all three of them."

Sherman was a former receiver under Jim Harbaugh at Stanford who became one of the great draft steals in the fifth round a year after Thomas and Chancellor came to Seattle. Carroll, familiar with Sherman from their shared time in the old Pac-10 Conference, called Sherman "unique and special" on draft day. He reiterated the team's commitment to selecting players with unusual traits, especially length. (K.J. Wright was another example that year.)

Sherman, taller than most cornerbacks at 6-foot-2, was the 24th of 37 corners drafted in 2011. This was before there were Carroll disciples such as Atlanta Falcons coach Dan Quinn, Los Angeles Chargers defensive coordinator Gus Bradley, Oakland Raiders defensive coordinator Ken Norton and San Francisco 49ers defensive coordinator Robert Saleh targeting similar corners for other teams. That is why Seattle wasn't especially worried about another team scooping up Sherman earlier. It seems improbable now, but I remember the Seahawks being at least as excited about Appalachian State safety Mark LeGree, whom they selected two spots after taking Sherman and who never played in an NFL game. That's how unpredictable these decisions can be on draft day.

It's easy to forget the Mark LeGrees of past drafts. It's also easy to forget that another corner Seattle selected that year, sixth-rounder Byron Maxwell, was ahead of Sherman on the depth chart in camp and might have gotten a shot at starting ahead of Sherman had he avoided injuries at the time. There was no holding back Sherman ultimately, but he plausibly could have landed on another team, in a different scheme, and never found the same opportunities.

Dominance in perspective

Since 2011, when Sherman joined a Seahawks roster already featuring Thomas and Chancellor, opposing quarterbacks have gone from being historically bad against a fully equipped LOB secondary to quite respectable when one or more of them come off the field.

Opposing quarterbacks have 83 touchdown passes with 109 interceptions on plays when Thomas, Sherman and Chancellor were all on the field together. This period spans 94 games and 2,869 pass attempts since 2011.

The numbers lend themselves to comical application. Seattle with those players on the field has allowed the following passing numbers on those 2,869 attempts:

59.4 percent completions, same as the career rate for Seneca Wallace

6.4 yards per pass attempt, same as the career average for EJ Manuel

2.9 percent touchdown rate, same as the career rate for Mike McMahon

3.8 percent interception rate, same as the career rate for Rex Grossman

71.2 passer rating, worse than the career rating for Luke McCown (71.3)

40.1 Total QBR, same as the career figure for Mark Sanchez

Put another way, the Legion of Boom has, on the whole, rendered all the quarterbacks it has collectively faced to become indistinguishable from those journeymen.

Remove Thomas, Sherman and/or Chancellor from the field, and the numbers over the same time period (since 2011) flip. Opposing quarterbacks have 41 touchdown passes with 17 interceptions on those plays.

The composite quarterback with numbers approximating those that opponents have put up against these incomplete LOB backfields averaged:

6.9 yards per pass attempt, same as the career average for Matt Hasselbeck

3.9 percent touchdown rate, same as the career rate for Alex Smith

1.6 percent interception rate, lower than the career rate for Tom Brady

89.2 passer rating, same as the career rate for Andy Dalton

58.7 Total QBR, about the same as the career rate for Carson Palmer

That's a big spike in opposing quarterback production when one of those LOB stars leaves the field. This game against Atlanta on Monday night will mark only the seventh since 2011, counting playoffs, in which Seattle has played even a single snap with Thomas on the field while Sherman and Chancellor are off it. That includes only 11 pass attempts over the past four seasons and zero over the past two.

"Do they get radical and try to have Earl down [in the box] sometimes?" an opposing coach wondered. "Or do they play the same stuff and let it ride? The big thing is, Dan Quinn knows everything they are supposed to do -- depth of alignments, footwork, techniques and what the disguises might look like if Seattle is going to try them, so it's a little tougher situation."

Seahawks with Legion of Boom since 2011 Stat All three

on field One or more

off field Pass Attempts 2,869 1,061 Yards/Pass Attempt 6.4 6.9 TD-INT 83-109 41-17 TD% 2.9 3.9 INT% 3.8 1.6 Passer Rating 71.2 89.2 Total QBR 40.1 58.7

Special ingredients: More than just talent

Kam Chancellor, left, has been cited by both players and front-office personnel as a leader and steadying force for the Seahawks. Christian Petersen/Getty Images

Each founding member of the LOB has brought something different to the team beyond his physical talent. Sherman thrives off confrontation, bringing an edge to the defense. Chancellor is the unquestioned team leader and tone-setting enforcer whose levelheadedness helps keep the more emotional Thomas on task. Thomas is widely regarded as the most intense player on the team, to the point that Sherman once joked in the spirit of those most-interesting-man commercials that "Practices watch Earl Thomas" rather than the other way around.

Thomas is the most athletically gifted of the three, as reflected by his status as the 14th player chosen in the 2010 draft. But as with Chancellor (2010 fifth-rounder) and Sherman (2011 fifth-rounder), he is known as much for his mindset as for his talent.

"The one thing that is interesting about those three guys is if you just look at them individually, they are able to carry the attitude and the mental toughness of a group," a coach from another team said. "That is really unique. You usually get one safety that is the tough guy, the ringleader. They have three guys like that. Thomas burns so intense on his off time that it overflows into the effect he has on the group when he is on his on time. That stuff matters more than anybody talks about it -- there is no gauge for it, so you can't debate it."

McCloughan compared Chancellor to former 49ers mainstay Justin Smith for the unquestioned leadership each provided.

"Kam is the leader not just of the defense, but of the team," McCloughan said. "That is what is going to hurt the most if he cannot play, is just that leadership on Sundays -- before the game, on the field, in the fourth quarter. If you pay attention to it, Earl is really hyper and flying around, and Kam is the one who settles him down and gets him lined up. They all listen to him. There is a story after I left there about how they were playing music in the locker room before a game and when Kam stepped up to say something, they turned the music off for him."

That word again: 'Unique'

Both McCloughan and the coach quoted above used the word "unique" in describing what went into the combined and individual makeup of the LOB. A second coach reached Sunday used the same word when asked about how Sherman, Thomas and Chancellor have helped Seattle execute coach Pete Carroll's defense.

"The unique thing they have been able to do in the NFL, they play with no disguise and they can beat you to the spot," this coach said. "They do what you are not supposed to be able to do, which is to say, 'I am going to be right here and I am going to paddle your ass.' The corners do some pressing and bailing, but Chancellor and Thomas say, 'Just so you know, I will be right here.' Then, when you get done playing them, they are who you thought they were. That is the biggest tribute that there is."

Sherman is the ball-hawking left corner who talked the talk before and after walking the walk. Chancellor built his legend on intimidation with a series of plays involving players such as Kellen Clemens, Jimmy Graham, Victor Cruz, Andre Ellington and Vernon Davis. Thomas is the human missile whose uncommon range makes the Seahawks' signature Cover 3 scheme work so well.

"All three of those guys tackle, and all three take the ball away," the same coach said.

Together, the LOB overwhelmed Peyton Manning and the Denver Broncos' record-setting offense in one Super Bowl and had Tom Brady on the ropes for three quarters of another. They've been part of a team that led the NFL in fewest points allowed four consecutive seasons before ranking third in 2016.

"When you get in a run formation, Chancellor plays like a linebacker," this coach said. "His ability to find angles in the box, to beat blockers with speed, the run-throughs, he is as effective as any linebacker. Then Earl Thomas has a great combination of the two things you want in a range player: the ability to make the hit that causes a dislodging of the ball, and then the ability to catch it. The league calls it 'blue' when you are the highest-ranking personnel at your position. He is so far freaking blue, it is ridiculous."

Then there is Sherman, whose 32 regular-season interceptions since 2011 are six more than any other player has collected. (Thomas' 20 are tied for fourth.)

"You knew every Sunday going in, he can take away half the field," McCloughan said.

The sun could be setting

Earl Thomas is the last Legion of Boom member standing, with long-term questions already being asked about Richard Sherman and Kam Chancellor. NFL Photos/AP Photos

Thomas has come back strong from the broken leg that ended his 2016 season prematurely and forced him to miss the final five regular-season games. While a hamstring injury sidelined him for the past two games, he is the youngest of the three LOB charter members at 28, having left Texas for the NFL after only two college seasons. His deal runs through 2018.

Sherman had never missed a game until his right Achilles tendon ruptured at Arizona in Week 10. His prospects for a full recovery appear strong, but he will turn 30 in March and will be entering the final year of a contract featuring $11 million in non-guaranteed salary. The Seahawks could bring him back and reassess based on how well Sherman performs. They could work out a new deal that lets him retire as a Seahawk, which would qualify him for having his No. 25 jersey retired if he reached the Hall of Fame. They could release him. What happens in free agency and the draft could affect their thinking.

Chancellor will turn 30 in April and is signed through 2020. It's unclear whether his neck injury will affect his long-term outlook. His contract carries millions in injury guarantees that convert to full guarantees after the Super Bowl, providing him some insurance if the injury prevents him from making a quick or full return.

Will Sherman return? Will Chancellor be OK? Is the LOB about to become a memory? No one could have plausibly predicted how all this would come together. There's no way to know how it will end, just that the end feels much nearer than it did even a week ago.