2012 NFL Free Agents: Key Role Players That These Offenses Can't Afford to Lose

They're not premier player on the offense like quarterbacks Tom Brady, Drew Brees or Eli Manning. However, role players must be effective in every opportunity they get.

After all, with limited chances to begin with there's even less room for error, enhancing the cost of each possession.

To that end, here are some key role players in free agency that their offenses can't afford to lose.

Mike Tolbert: RB, Chargers

He's not the fastest or most explosively dominant running back, but San Diego has found a versatile threat in Mike Tolbert.

Last season he accounted for 490 rushing and 433 receiving yards and managed to score 10 total touchdowns (led team) and convert 48 first-downs (third on team).

In any short yard situation, Tolbert has the ability to blast for a first-down, break a big run or make a few defenders miss en route to picking up solid yards after the catch. He's a complete player, a dual-threat back, and a proven playmaker.

Tolbert has also proven effective as a blocker in the Bolts' pass-heavy attack.

Mario Manningham: WR, Giants

Despite being mainly a reserve or role-playing receiver, New York's Mario Manningham provides Eli Manning with another reliable target in the Giants pass-oriented offense.

Manningham's presence when the Giants lineup in three/four-wide sets is arguably more imposing than Hakeem Nicks or Victor Cruz because Manning knows that Mario isn't seeing double coverage.

In the postseason, Manningham made his biggest impact by catching a touchdown in three of the Giants four games while making a spectacular sideline grab in front of Bill Belichick. His lone reception against San Francisco in the NFC title game was a 17-yard touchdown catch that gave New York a fourth-quarter lead.

If the Giants let Manningham leave this offseason, they'll feel the loss of the dynamic vertical threat, plus some of their experience and depth at the receiver position.

BenJarvus Green-Ellis: RB, Patriots

Not a utility player like Mike Tolbert, "The Law Firm" is a bruising every down back in a Patriots offense that uses numerous players to function properly.

BenJarvus Green-Ellis has the unenviable job of battling in the trenches for New England, gaining 667 rushing yards on 181 attempts. He averaged only 3.7 yards per carry, however he scored 11 times last year.

He also served as a viable check down safety outlet for Tom Brady, catching nine passes for 159 yards and adding three scores. That said, Green-Ellis isn't a game-breaking back.

BenJarvus's role is to work the middle, find a gap and take any would-be tacklers with him downfield. It's a dimension that none of the other Pats running backs can bring to the table and losing him would only make their offense more susceptible to a solid pass rush.

Scott Chandler: TE, Bills

Definitely not one of the more well-known tight ends in pro football, but Buffalo's Scott Chandler has quietly developed into a complete NFL player.

As a receiver, Chandler was a reliable threat over the middle with 38 catches for 389 yards and six touchdowns (second on team). Plus, 25 of his 38 receptions moved the chains, helping Buffalo's offense move effectively early in the season.

The Bills have a solid offensive line to bolster the running game, but Chandler's 6'7", 260-pound frame makes him like a sixth offensive lineman. Backup running back CJ Spiller picked up where Fred Jackson left off after he went down thanks in part to Chandler's run-blocking.

Looking ahead to 2012, Buffalo must retain Chandler to have any shot at scoring once inside the red zone and to move the chains on third down. When quarterback Ryan Fitzpatrick struggles, he must look in Chandler's direction.

John Rozum on Twitter.