The Chiefs, by age, had the second youngest roster in football last year.
The defense, especially so.
Starting from the back, Kansas City fielded three rookies: Eric Berry, Javier Arenas, and Kendrick Lewis. All of them ended up grading above-average in the league according to profootballfocus.com.
Eric Berry appears to be an absolute home run, having played every defensive snap for the 2010 season, which is obviously incredible for a rookie. His presence payed large dividends, especially in the run game, and in particular a midseason victory over the Bills where he came up with a game-winning interception to halt the drive.
A lot of credit is still due to the other two, however. Kendrick Lewis was better in coverage than Berry, and ended up playing twice as many snaps (879) as veteran teammate Jon McGraw. This duo could become one of the very best at the safety positions as soon as next year, much in the same way that Troy Polamalu and Ryan Clark are for the Steelers.
Arenas was the primary nickleback for the Chiefs, and served admirably. He was never a liability in coverage from the slot, and consistently made tackles that stopped first downs. He was also a dual-threat as a returner, and we should see a marked improvement in both of those areas for him next year.
The most exciting part of the Chiefs' young secondary, however, comes from the cornerback tandem of Brandon Flowers and Brandon Carr. Flowers is becoming one of the elite cornerbacks in the league. His numbers prove it too, owning one of the best success rates in the league, and is one of the surest tacklers. He allowed only 50.1 percent of passes to be caught that were thrown his direction, and allowed only 81 yards after the catch, one of the lowest in the league.
Carr owns the fourth-best burn rate in the league, allowing only 45.4 percent of passes to be caught by the receiver.
In the front seven, Tamba Hali, Glenn Dorsey and Derrick Johnson are dominant.
Hali has established himself as one of the best pass-rushers in the league, second only to DeMarcus Ware. Dorsey saw significant progress last year and given that he had a breakout season, we can expect big things from him for years to come. Derrick Johnson is simply a force against the run, and is a linebacker you can rely on to fall into coverage.
The combination of the back end and the front end last year was phenomenal in some games. In others, there were lapses. Second-year players such as Jovan Belcher, as well as the rookies tend to make mistakes. There were flashes of absolute dominance in some games, particularly against the 49ers in week three.
The defense's most significant loss from last year was Mike Vrabel, whose leadership will surely be missed. However, Andy Studebaker has shown that he can be quite disruptive in the little time he's been on the field and with the lockout dragging on so long, he will inevitably get the nod to start over rookie Justin Houston.
With one more year of experience, this defense will only continue to get better. If Kelly Gregg is healthy, he could be the edge this defense needs to put them over the top. Tyson Jackson was drafted third overall in 2009 and while his rookie year was awful, he made significant strides in 2010 after he came back from injury. If he improves, the two first-rounders on the defensive line will create nightmares for opposing defenses and make a promising young secondary look even more terrifying.