2012 NFL Free Agents: Key Defensive Players These Teams Can't Afford to Lose

In order to continue keeping up with the Joneses so to speak, NFL defenses can really gain an edge over the offense-dominated movement by retaining key defensive players.

Regardless of position, it simply comes down to having a set of players that have already built a solid amount of chemistry. If anything for a defense, working in sync can only increase its odds versus any offense.

That said, here are some key defensive free agents that their franchises can't afford to lose.

Calais Campbell: DE, Cardinals

On a team that finished the season 7-2, Arizona's Calais Campbell is arguably their best defensive player on a unit that really improved down the stretch.

Every year he has been in the league, Campbell has simply gotten better. His tackles totals have risen from 48 in 2009, to 60 in 2010 and closed out with 72 in 2011. Not to mention he has accumulated 21 sacks during that three-year span as well.

Campbell also has great instincts when pass rushing, and it really showed in 2011. There, Campbell defended 10 passes after just eight from his first three seasons.

Despite getting snubbed from the Pro Bowl in 2012, provided that Campbell keeps improving, the Cardinals will have another legit shot at the playoffs and next fall will get the franchise back on track.

D'Qwell Jackson: LB, Browns

Other than cornerback Joe Haden, Cleveland linebacker D'Qwell Jackson is the Browns' only consistent defensive player. Now, they do have two decent players in Jabaal Sheard and Phil Taylor along the defensive line, but their production still doesn't compare to Jackson's as part of the front seven.

Last season D'Qwell recorded 158 tackles (116 solo), 3.5 sacks and recovered three fumbles. He isn't an overly dominant presence in the middle but the numbers prove Jackson's value at stopping the run.

In other words, if the Browns lose him this offseason they'll have to start all over with a new run-stuffer. And, for as bad as Cleveland was at stopping the run in 2011 (ranked No. 30), Jackson was the Browns only hope against it.

As for 2012, Jackson heads in with 565 career tackles and, provided that Sheard and Taylor continue solid development, D'Qwell will flourish even more at controlling the middle of Cleveland's defense.

Brandon Carr: CB, Chiefs

Despite losing safety Eric Berry as part of one of the better secondaries in the game for 2011, corner Brandon Carr proved himself by intercepting four passes and defending 15.

With Brandon Flowers playing opposite him, Carr is part of a great cornerback tandem that led the K.C. defense to a No. 6 ranking against the pass. 2011 was also the third straight year where Carr defended at least 15 passes (25 in 2010, 19 in 2009).

Having now played with Flowers since 2008 (each players' rookie season) and Berry in 2010, Kansas City losing Carr would be missing an enormous piece to its defensive puzzle.

Considering that Carr is 6' and weighs over 200 pounds, he's a big, physically imposing corner who can jam at the line and lock down most No. 1 receivers. The Chiefs have a lot to hope for in 2012, as 2011 was almost over before it started thanks to a plethora of key injuries, and retaining Carr must be a top priority.

Jim Leonhard: Safety, Jets

He certainly isn't the most well-known safety in the league, nor does he look physically imposing. Still, the Jets' Jim Leonhard is one of the most important parts to Rex Ryan's defense.

With corner Darrelle Revis locking down one half the field, Leonhard is responsible for anything opposite Revis as well as over the top. He may only be 5'8" and close to 190 pounds, but Leonhard easily has some of the best instincts in the game (185 tackles, 15 passes defended since 2009).

And despite his size, Leonhard has also proven to be a reliable roll down safety to cover slot receivers, running backs and help with run support. He's also a great underneath zone defender when Ryan blitzes his linebackers.

Keeping Leonhard in New York is a must for Gang Green to remain a top NFL defense. With him, Revis and Antonio Cromartie, the Jets still have one of the best secondaries in pro football. 

John Rozum on Twitter.