Patriots quarterback Tom Brady and Chargers quarterback Philip Rivers speak at midfield after a 2017 game at Gillette Stadium. Rivers declared for free agency on Monday; Brady could do the same before March 18. AP Photo/Steven Senne

The formal separation of Philip Rivers and the Los Angeles Chargers is not a surprising occurrence, and yet the franchise’s announcement Monday afternoon still hit like a shock wave. It represents both the departure of a franchise-defining pillar and the likely beginning of a fevered offseason for quarterback movement.

In a statement on the Chargers’ website, General Manager Tom Telesco said Rivers and the Chargers mutually decided to “turn the page on what has truly been a remarkable run.” Rivers, 38, said after the season finale he plans to keep playing, even if it’s not for the only team he has known in a 16-year career. His official departure is the first shoe to drop in a spring that promises to rearrange the league’s quarterback landscape.

Rivers is going to play for a team other than the Chargers next season, which counts as momentous all by itself. The Chargers without Rivers is a completely foreign concept to a generation of football watchers. Rivers took over as the Chargers’ quarterback in 2006 and started all 224 games since. His 123 victories rank ninth all-time. He outlasted three coaches and one city. The Chargers have been in existence since 1960, and Rivers has started 24.4 percent of their games.

The Chargers went 5-11 last year, and on the verge of entering a new stadium they will share with the Rams, the franchise has made essentially no impact in Los Angeles. Rivers is the Chargers, but the Chargers have little use for a 38-year-old quarterback coming off a losing season who has already failed to excite a fan base it is not reaching.

“Philip can still compete at a top-starter level and, in a perfect world, number 17 is your quarterback forever,” Telesco said in his statement. “Obviously, we live in an imperfect world where the only constant is change.”

What Rivers’ departure means for the franchise is most poignant, but what it portends for the league will reverberate beyond southern California. The NFL is entering the offseason with an uncommon, perhaps unprecedented, confluence of highly qualified free-agent quarterbacks and highly sought passers in the draft.

Tom Brady’s contract is up, and signs point to him reaching free agency for the first time in his career, at age 43. Ryan Tannehill, last seen quarterbacking the Titans to the AFC championship game, could be a free agent. So could Teddy Bridgewater and Jameis Winston. Andy Dalton and Cam Newton, two franchise pillars in their own right, may end up as trade fodder.

Joe Burrow is the likely first overall pick, to the Bengals, and teams will maneuver to draft Alabama’s Tua Tagovailoa and Oregon’s Justin Herbert behind them, with Utah State’s Jordan Love also a tantalizing, if less proven, prospect.

All those quarterbacks need teams to play for, and the openings will be there, even among teams not about to lose a quarterback to free agency. The Colts may decide they can improve on Jacoby Brissett, even though he ably stepped in after Andrew Luck’s retirement. Ryan Fitzpatrick is a player you want in your locker room, but he is not a long-term answer in Miami. Jon Gruden is always restless with quarterbacks, and he just watched Derek Carr oversee a second-half collapse right before the Raiders move to a new city and a fan base that needs to be won over.

Making a list heavy on speculation, then, the Chargers, Patriots, Panthers, Dolphins, Buccaneers, Titans, Bengals, Colts and Raiders all will or could be making a change at quarterback by importing one currently outside their franchise.

And that may not even be a complete list. Will the Lions decide Matthew Stafford has taken them as far as he can and entertain trade offers while finding their future quarterback with the third pick in the draft? The Jaguars just signed Nick Foles last year, but the top executive who signed him, Tom Coughlin, is gone, and Jacksonville may feel pressure to make a splash.

The Saints, too, are a special case. Drew Brees, 41, has not yet made a final declaration of his intentions for next season. Bridgewater is a free agent and Taysom Hill is a restricted free agent. How all those pieces fit together will be a subplot to watch.

All of that will play itself out over the next two months. We know now, though, that Rivers will find a new team. It is worth wondering what kind of place Rivers has in the current NFL, where a quarterback’s ability to steal yards on the ground and keep plays alive has never been more paramount. There is still little doubt he’s one of the 32 best in the world at what he does.

Rivers makes a lot of sense in Tampa Bay, a team with lethal wide receivers, an opening behind center and, in Bruce Arians, a quarterback-friendly coach who once revived a late-career Carson Palmer – another brainy, immobile passer. Rivers played his college ball at North Carolina State, and if the Panthers doubt Newton’s health or simply want a restart under a new coach, maybe Rivers could be a one-year stopgap in Carolina.

Rivers’ next team will provide plenty of intrigue. Even though it could be seen coming, it seems strange that there will be a next team for him, that Rivers will wear a uniform other than the Chargers’.

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