High turnover continues at RB

Recently rewarded with a contract extension befitting a man who has logged more than 2,000 carries and is probably only a half-season shy of cracking the 10,000-yard rushing mark, Fred Taylor realized even before this offseason that he had beaten the odds for longevity at a position with the NFL's shortest shelf life.

But the events of the past week -- in which veteran tailbacks have changed teams via trades and free agency more than some runners change direction on an 80-yard touchdown gallop -- have brought an even more sobering reality for the Jacksonville Jaguars' star.

In terms of continuous service to one franchise as its feature runner, heading into his 10th season with the same team, Taylor is the king of current NFL tailbacks. Which means that he is also just one injury shy, or the loss of a half-step removed, from becoming the tailback equivalent of a tyrannosaurus.

"The way [running backs] are moving around right now," Taylor said, "it makes you feel a little bit like a dinosaur."

Indeed, in the ongoing evolution of the tailback spot, this offseason appears to have morphed into the "era of the disposable runner."

Eight teams have either traded or permitted to depart through free agency tailbacks who were their leading rushers in 2006. With more moves to come, at least a dozen teams are projected to have new starting tailbacks in 2007. It appears that just 10 franchises in 2007 will have the same starting tailback for the third season in a row. Little wonder guys like Taylor, Warrick Dunn of Atlanta and Seattle's Shaun Alexander feel a bit out of place anymore.

It's because tailbacks can't seem to stay in the same place for any length of time now.

Thomas Jones resurrected his career in Chicago but, with former first-rounder Cedric Benson apparently ready to step into the starting lineup, the Bears had no qualms about dealing their No. 1 tailback to the New York Jets. Buffalo officials felt Willis McGahee would be impossible to keep around when his contract was up after the coming season, so they traded him to Baltimore rather than have him escape through free agency next spring. The Denver Broncos, who regularly manufacture 1,000-yard rushers from middle-round picks, shipped off Tatum Bell to Detroit as part of the trade to land cornerback Dre' Bly.

Among the free agents who have changed teams so far, or are in the open market, are Jamal Lewis, Ahman Green and Corey Dillon.

Only three seasons ago, Lewis ran for more than 2,000 yards, but that feat is a distant memory now. Less than two months after rushing for 113 yards in Super Bowl XLI, and nearly winning most valuable player honors in the title game, former Indianapolis starter Dominic Rhodes went from a title team to the Oakland Raiders, the club with the league's worst record in 2006. Green's exit from the Packers came after he had rushed for 1,000 yards in six of seven seasons.

It's the continuation of a recent but well-defined trend in which teams have promulgated a revolving door policy at tailback.

Last spring, for instance, the Colts opted not to keep Edgerrin James, because they felt there was too much tread rubbed off the tires. So they allowed him to depart through free agency, invested a first-round choice for Joseph Addai, teamed the rookie with Rhodes in a time-sharing arrangement, and finally won the Super Bowl title that had escaped them during James' tenure with the franchise.

"It just seems there's a feeling now like, 'Use 'em up and spit 'em out,' you know?" said James, who signed a lucrative contract with the Arizona Cardinals. "You reach a certain point with a team and they decide that's it, that they want to get younger or whatever. You're just not going to see [running backs] have long careers in the same place, the way they used to."

It's almost as if corporate philosophy at the position finally has caught up to all of the actuarial tables.

For years, NFL Players Association surveys have indicated that the running back spot has the shortest career span of any position in the league. So teams now are trying to stay a step ahead of the curve, disposing of tailbacks before they wear out, rather than waiting for the obvious signs of erosion.

And because running back is a position at which the skill-set doesn't change at any level of the game, with the exception of having to pass protect more in the NFL, coaches and scouts feel there is always a ready reservoir from which to draw replacements. Some teams now assume they can draft a runner, use him for four or five productive seasons, discard him, and draft another one.

Such a mind-set certainly has contributed to the wholesale migration of runners witnessed over the past week. The other factor is that franchises aren't going to make major investments to retain veteran tailbacks, players who are one sprained ankle or a shredded knee ligament away from oblivion, if there are replacements available to them.

It's meant incredible turnover, especially in the past three springs, at a position once noted for its stability.

"If a team senses that you're getting to the point where you're used up, right or wrong, they're going to find someone else to run the football for them," said Travis Henry, who has posted 1,000-yard seasons in Buffalo and Tennessee, and will try to do so with the Broncos now, after signing there as a free agent last weekend. "That's just how it is anymore."

Len Pasquarelli is a senior writer for ESPN.com.