Melvin Gordon's prolonged holdout and Derwin James' foot injury in L.A., Antonio Brown's head-to-toe spectacle in Oakland, and a spinning turnstile of head coaches and quarterbacks in Denver all complicate efforts to unseat the Kansas City Chiefs in the AFC West.
Not that it's status quo in KC. The Chiefs' defensive makeover features new coordinator Steve Spagnuolo and as many as eight new starters.
Patrick Mahomes, the MVP who threw for 5,000-plus yards and 50 touchdowns in his first season as a starter, never touched the ball in overtime of the AFC championship because Kansas City's defenders couldn't get off the field against the Patriots after New England won the coin toss.
That rendered the biggest breakout star of 2018 another sad spectator at Arrowhead Stadium as Tom Brady and Bill Belichick hoisted their ninth Lamar Hunt Trophy together.
"We were super close," Mahomes said. "We fell just short."
Mahomes has just about everyone back in his quest to get the Chiefs to their first Super Bowl in 50 years, including star receiver Tyreek Hill , cleared to play by the NFL following an offseason domestic violence investigation.
Among the Chiefs' new defenders are free safety Tyrann Mathieu and pass rusher Frank Clark, who replaced Dee Ford, whose offside penalty in the AFC championship negated Charvarius Ward's interception in the final minute of regulation.
As painful as that loss was, coach Andy Reid called it "a great learning tool."
"I think it's great for our football team to have that opportunity, to see the intensity that it takes to play at that level," said Reid, whose Philadelphia Eagles lost three straight NFC championships before breaking through with a trip to the Super Bowl following the 2004 season.
The Chargers are the Chiefs' biggest threat in the AFC West, where Denver and Oakland continue rebuilds:
The Chargers are considered one of the AFC's top teams, but they didn't have a smooth summer with Gordon's holdout; left tackle Russell Okung missing camp with blood clots; wide receiver Keenan Allen dealing with an ankle injury; and safety Nassir Adderley, a second-round pick, hampered by a pulled hamstring.
Then James, their All-Pro safety, broke his right foot at a practice against the New Orleans Saints in mid-August and required surgery that's expected to sideline him for at least three months. He'll be replaced by Adrian Phillips.
This is the second straight year the Chargers go into the season without one of their top defenders. Pass rusher Joey Bosa missed the first nine games last season with turf toe, although Philip Rivers led Los Angeles to a 7-2 start on its way to a 12-4 season before the second-round exit from the playoffs.
The 17th overall pick in 2018, James made a team-high 105 tackles to go with four interceptions, 3½ sacks and 13 pass breakups his rookie season.
Gordon's holdout ahead of the final year of his rookie contract allowed Justin Jackson and Austin Ekeler to show why they should be in the mix for more carries in 2019.
Joe Flacco is the latest in a long line of quarterbacks Broncos GM John Elway has acquired since Peyton Manning's retirement in 2016.
"It's a hard position to fill," Elway said. "We tried to shake all these trees around here the last four years and quarterbacks didn't fall out of it."
Saying Flacco is in his prime at age 34, Elway might be trying hard to sell his latest QB acquisition to an antsy and skeptical fan base that suffered through flops by Mark Sanchez, Trevor Siemian, Brock Osweiler, Paxton Lynch, Case Keenum and Chad Kelly.
No matter the motivation, Flacco appreciates Elway's flattery.
"I definitely feel that way," Flacco said. "So it feels good to hear somebody say that. I mean, shoot, with Tom Brady now, quarterbacks are playing until they're about 60 years old."
Speaking of sexagenarians, Elway's latest head coach is 61-year-old rookie Vic Fangio , the architect of the Chicago Bears' stingy defenses from 2015-18, who replaced Vance Joseph (11-21 in two seasons).
When Brown arrived at training camp for the Raiders in a hot air balloon, coach Jon Gruden joked he expected more drama from his star receiver.
Brown provided that drama by missing significant practice time dealing with frost-bitten feet suffered while getting cryotherapy treatment in France, and waging a battle with the NFL over the use of his outdated helmet.
He lost a grievance to allow him to use the helmet that's no longer certified as safe and returned to camp. But after he skipped another workout, general manager Mike Mayock issued an ultimatum for Brown to be "all in our all out."
The Raiders acquired Brown from the Pittsburgh Steelers as the cornerstone to an offensive upgrade around Derek Carr that also features first-round running back Josh Jacobs, deep-threat receiver Tyrell Williams, and elite pass blocker Trent Brown.
An improved offense won't matter much if the Raiders can't also upgrade a pass rush that generated an NFL-low 13 sacks last season after trading away star Khalil Mack.
PREDICTED ORDER OF FINISH
Chiefs, Chargers, Broncos, Raiders
AP Sports Writers Dave Skretta, Joe Reedy and AP Pro Football Writer Josh Dubow contributed.
Follow Arnie Melendrez Stapleton on Twitter: http://twitter.com/arniestapleton