Kansas City Chiefs (2011 record: 7-9)
What went wrong?:

After a 4-12 showing in 2009, Kansas City would surge to the top of the AFC West a year later, going 10-6. There were two key components to this turnaround: an offense that flourished under Matt Cassel, whose spectacular season was comparable to his 2008 emergence in New England, and new defensive coordinator Romeo Crennel vastly increasing production on his side of the ball.
For Cassel, his 27 touchdown passes versus 7 interceptions were a far cry from his pitiful first year in Kansas City. He also had the luxury of a two-headed running back system with veteran Thomas Jones and third-year upstart Jamaal Charles, who combined for over 2300 rushing yards and 11 touchdowns. Dwayne Bowe put up fifteen touchdowns, and rookie Dexter McCluster served as a potent punt returner (15.5 yards a return). McCluster was also a source of frustration and caution for defenses, as his speed worked in decoy situations.

In Crennel’s first year overseeing the D, he reduced the points allowed by a nearly a full touchdown (26.5 to 20.4 per game). The defense as a whole became hungrier, going from twenty-two sacks in 2009 to thirty-eight in 2010. Tamba Hali benefitted the most from Crennel’s form of attack, putting up 14.5 sacks, seven more than his previous season high. Veteran Derrick Johnson emerged into a true do-as-I-do leader, the way Roman Phifer and Tedy Bruschi were on Crennel’s Patriots. Rookie Eric Berry’s performance at safety (72 tackles, 2 sacks, 4 INT, one for a touchdown) helped anchor the defensive turnaround.
2011 was a different story. While the defense remained strong (21.1 points per game allowed, twelfth best in the league), the offense went into a complete nose dive.
Jamaal Charles, who came off over 1400 yards in 2010, tore his ACL in the second game of the season against Detroit, and was done for the year. 33-year-old Thomas Jones started eight games, mustering only 3.1 yards a carry. Jackie Battle emerged as the best available option, putting up 600 yards and two rushing TDs, but it was a far cry from the downhill explosion that Kansas City boasted a year earlier.
In addition, tight end Tony Moeaki, who was highly productive as a rookie in 2010, injured his knee in preseason and was also lost for the year.
As for Cassel, his slow start led to the Chiefs going 0-3. In those losses, Cassel threw three touchdowns, five interceptions, and a wretched 428 yards. To his credit, he led the team to four straight victories afterward, giving Kansas City hope at 4-3. After losing to the Dolphins a week later, Cassel suffered a hand injury in a loss to Denver on November 13. That injury landed him on IR, leaving Tyler Palko and former rival Kyle Orton to carry on.
The offense could only muster 13.2 points per game, the second worst average in the league.
Injuries weren’t exclusive to the offense. Eric Berry tore his own ACL after a cut-block from Bills wideout Stevie Johnson on opening day. Like every other injury mentioned so far, you can guess how this one goes: Berry was done for the year.
After a blowout loss to the Jets on December 11, which dropped the Chiefs to 5-8, Kansas City fired head coach Todd Haley. Haley’s relationship with GM Scott Pioli was tense and full of disagreement. Rumors had even swirled that KC wanted to dump the abrasive, risk-taking Haley after the 2010 playoff season.
But the downward spiral of 2011 provided Kansas City’s front office with the bullet they needed to make the mid-season change.
What have they done to fix it?:

With Haley gone, Romeo Crennel took the reins to finish out 2011. While his career as a defensive coordinator and assistant earned him five Super Bowl rings with the Giants and Patriots, his four-year run as Cleveland’s head coach in the mid-2000’s has been his career’s only blight. Going 23-41 with the accursed Browns, with one winning season in 2007 that fell just short of the playoffs, the team would wind up in the bottom three in points scored three out of the four years. For a defensive guru, his Browns sure gave up a lot of ground on that side of the ball as well.
None of that past mattered in Crennel’s first game coaching the Chiefs. To the shock of the majority, Kansas City knocked off the 13-0 defending champion Green Bay Packers, 19-14. Aaron Rodgers, that year’s MVP, completed less than 50% of its passes. The Packers were held to less than twenty points for the one and only time that season. Rodgers was sacked four times (three for Hali), and the defense forced two fumbles. Green Bay never got comfortable, and they were even shut out in the first half.
After the game, Crennel received a Gatorade shower from his players, even though he’d just led them to a 6-8 record. It was symbolism: Haley’s confrontational approach was gone, and Crennel’s confident X’s and O’s tormentum had just beaten the best team in the league.
The Gatorade may as well have been Kool-Aid, and the players were downing it in spades, buying into the new boss.
The Chiefs lost a close one to Oakland the following week, but held Denver to three points in the victorious finale. With the players behind him, the Chiefs promoted Crennel to head coach for 2012. He also retains his defensive coordinator title, and for good reason.
Kansas City gets Cassel, Charles, Moeaki, and Berry back from their injuries, which will provide a fresh start for a team that had enough holes to make Swiss cheese.
Kansas City didn’t make too many offensive upgrades, but instead they purchased insurance. Should Charles or Moeaki go down to injury again, suitable back-ups await. Behind Charles is former Madden cover-model Peyton Hillis, who tries to shake off a disappointing and drama-filled 2011 with the Browns. With that behind him, the “Arkansas Avalanche”, coupled with a healthy Charles, could revive the crushing running attack that Kansas City offered up in 2010.
As for Moeaki, Kevin Boss will be his understudy. Boss’ blocking skills, which were displayed in four seasons with the Giants, add another dimension to the promising running game.
And speaking of blocking, what about this coup: the Houston Texans released durable and monstrous offensive tackle Eric Winston, who started sixteen games in every season from 2007 through 2011. The release was contract-related, and KC gobbled him up in a hurry. If the running upgrades already mentioned weren’t good enough, Winston, who blocked successfully for Steve Slaton and Arian Foster in their best years, puts them over the top.
And since Crennel knows defense, he made a huge (literally) pick-up on draft day. Dontari Poe was selected as the 3-4 defensive tackle of Crennel’s dreams: a 346 pounder with exceptional speed and power. Although his college output was considered disappointing, his raw athletic skills have led some to give him a ceiling on the level of Haloti Ngata.
2012 outlook:

Kansas City’s simply overlooked because Peyton Manning is in Denver, drawing all the headlines. Factor in San Diego as a typical choice for success (despite recent lackluster seasons), and Oakland putting pieces together, and you can see how Kansas City might get squeezed out of the picture. But the Chiefs who captured the division in 2010 are all healthy, as of right now. They’ve added pieces on offense that make their running game a nightmare, and Romeo Crennel, as head coach, will have full say over how hard the defense, his defense, will attack.
And hey, remember that classic Patriots-Colts rivalry? When Crennel was defensive coordinator in New England, Peyton Manning could never beat them. The Colts, usually a high-powered offense behind Manning, could only score more than thirty points once. The Patriots were 6-0 in that stretch, winning by a combined score of 191-105, or 32-18 on average.
Even in the two times they met as Crennel coached the Browns, the Colts did win both games. But for their part, the Colts only scored 13 and 10 points respectively, and those were sub .500 teams Peyton Manning was up against.
Those who think Manning and Denver have the drop on the division opposition, don’t forget that one defensive coordinator who made his life a living Hell.