This NFL season has been defined by the top contenders getting upset by far lesser teams. The result is more parity than we’ve seen in years, with only one team — the 9-2 Arizona Cardinals — entering Week 12 with fewer than three losses.

While that parity keeps the playoff hopes alive for many, there are several teams — both those firmly in the postseason picture and those that are at risk of falling out of it — whose seasons haven’t gone according to plan. Let’s take a look at what is plaguing five struggling teams and whether any of them can turn things around:

Seattle Seahawks: In the first half of the 2020 season, Russell Wilson was the MVP front-runner. It appeared Seattle had finally decided to “Let Russ Cook,” and he was burning up the league as the Seahawks got off to a 6-1 start.

But as the season went on, opponents adjusted. Many teams played a cover-two defense that limited Wilson’s ability to get the ball consistently to wide receivers DK Metcalf and Tyler Lockett. Seattle finished with a 12-4 record but lost in the first round of the playoffs.

This season, the offense has been a disaster en route to a 3-7 start. Part of that was because of an injury to the middle finger of Wilson’s right hand that caused him to miss three games, but in the two games he has been back, the offense has gotten even worse. Wilson has done poorly on third down and in the red zone, and his offensive line has struggled to pass-block.

That is putting a strain on Seattle’s defense, which has been on the field way too much and has worn down in the fourth quarter.

The Seahawks aren’t out of the playoff picture yet, given the state of the NFC wild-card race. They are only two games out of the sixth seed, but there is a logjam of teams in front of them. To have any chance, they’ll need to get Wilson back on track — starting with Monday night’s game at Washington.

Buffalo Bills: For the season’s first two months, the Bills looked like the AFC’s No. 1 seed. But they have lost three of their past five games, and they haven’t looked good in the process. They had an embarrassing 9-6 loss at Jacksonville in Week 9, and on Sunday the Indianapolis Colts blew them out, 41-15.

The prevailing thought is that opponents have figured out the Bills’ offense. Quarterback Josh Allen was unstoppable last year, throwing for 4,544 yards and 37 touchdowns while completing 69.2 percent of his passes. But things haven’t gone as smoothly this year. Allen has four touchdowns and five interceptions over the past three games. The offensive line has been okay but not great. Perhaps most importantly, Buffalo’s running game has been close to nonexistent. This has allowed opponents to defend only the pass — often using zone coverage with two deep safeties to prevent big plays.

The Bills have a great coaching staff, but they will need to adjust their strategy in their final seven games. The New England Patriots, on a four-game winning streak, have surpassed them for first in the AFC East. Buffalo is still a playoff team, but its chances of making a deep run could be tied to whether it wins the division and gets a home playoff game.

Chicago Bears: They had to know going into the season that they would have one of the NFL’s worst offensive lines after letting go of tackles Charles Leno Jr. and Bobby Massie and losing rookie Teven Jenkins to injury. That caused problems for quarterback Andy Dalton, who hurt his knee scrambling to avoid a sack, and it has destroyed the rookie season of Justin Fields. The first-round pick is guilty of hanging on to the ball too long, but he has been sacked 31 times in 10 games (eight starts) and suffered a rib injury during Sunday’s loss to the Baltimore Ravens.

The offense is a mess. The Bears are averaging just 16.3 points, and Fields has thrown for four touchdowns against eight interceptions while rarely using his speed in the running game. The defense also has struggled, and edge rusher Khalil Mack is out for the season with a foot injury.

Add it all up, and Coach Matt Nagy will have a tough time keeping his job.

New Orleans Saints: Sean Payton was perhaps the Coach of the Year front-runner after getting the Saints off to a 5-2 start. What he accomplished with a roster depleted by injuries, salary cap casualties and Drew Brees’s retirement was remarkable.

But over the past three weeks, everything is catching up to the Saints. They’ve lost three in a row, all started by quarterback Trevor Siemian after Jameis Winston blew out his ACL in a win over the Buccaneers, and the absence of star wideout Michael Thomas, who will miss the entire season because of injury, has been noticeable.

It hasn’t helped that star running back Alvin Kamara, also the team’s receptions leader, has missed the past two games with a knee issue or that injuries are piling up on the offensive line.

The upcoming schedule is tough on the Saints. They play the Bills on Thanksgiving, followed by the Dallas Cowboys the following Thursday and the Bucs two weeks after that. As one of three NFC teams at 5-5, they’re still right in the middle of the playoff picture, but that might not be true four weeks from now.

Pittsburgh Steelers: They are still in the playoff race at 5-4-1, but the underlying signs are concerning. All five of their wins have been one-possession games, including one that went to overtime. Their point differential is minus-12.

Quarterback Ben Roethlisberger has done his best to keep the team above .500, but he isn’t the Big Ben of old, and the revamped offensive line has struggled, allowing Roethlisberger to be sacked 21 times in nine games. He’s having to get rid of the ball quickly, averaging only 6.6 yards per attempt. Rookie running back Najee Harris is carrying a heavy workload, but he’s averaging just 3.6 yards per carry.

The biggest concern might be the schedule. It’s the second-toughest in football through the end of the season, with games against the Cincinnati Bengals, Ravens (twice), Minnesota Vikings, Tennessee Titans, Kansas City Chiefs and Cleveland Browns.