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[Ed.'s Note: In the latest issue of the Mag we've got a feature on Buc's back Earnest Graham: TEN MIL THE HARD WAY. He figures into the evolving multi-back system in Tampa as Cadillac Williams gets healthy. Mag associate editor Jordan Brenner decided to thus explain the trend in multi-back offenses in his latest entry of Settling The Score.]

"If you have two, then you don't have one." It's one of those trite football sayings with a simple meaning—if you're playing two guys, that's because neither is good enough. While the phrase most often applies to quarterbacks, running backs have not escaped being viewed through the same lens. That's changed, though. A more accurate phrase these days might be: if you don't have two, you're probably in trouble.

You don't have to be a fantasy nut to notice the NFL's trend toward time-share backfields. Still, Matthew Berry and ESPN Researcher Jason Vida show the extent of the change, demonstrating that last season, "NFL teams gave fewer carries to their leading rusher and more carries to their second backfield option than in any of the past 10 seasons."

That trend will only be more pronounced this season (much to the chagrin of fantasy owners). But seemingly more important is what this change actually means for real football teams. So let's start with a shocking statistic: Five of the last six Super Bowl champions featured time-share backfields.

Is that causation or correlation? We'll see. At the very least, we can conclude that time-share backfields don't preclude success. But do they drive it? Let's examine the four main reasons (generally) given for splitting carries and see where they lead.

1) Splitting carries pays off late in the game.
As Titans coach Jeff Fisher says, "You want your back fresh in the fourth quarter and in the four-minute situation." It's a reasonable expectation, but it's not supported by stats. From 2003-07, the performance of RBs hardly changed as the game wore on, meaning there's little reason to limit carries:

Keep in mind that most coaches, personnel people and—especially—the runners themselves argue that backs need carries to get in a groove. Says Bengals back Rudi Johnson: "You've got to have a rhythm to see how the defense is playing. You have to set a tempo. Everyone knows I get stronger as the game goes on; that's my forte."

And the five RBs who carried the ball most often last year (Clinton Portis, Edgerrin James, Willie Parker, LaDainian Tomlinson and Thomas Jones) didn't demonstrate any kind of a solid workload trend. Three increased their yards per carry in the fourth quarter, while two declined. So, it's tough to isolate fourth quarter fatigue, at least in the regular season.

2) Time-shares keep backs fresh later in a season.
Players on both sides of the ball are faster and stronger than ever before, meaning contact is more vicious. Chiefs GM Carl Peterson sums up this perspective: "The position is evolving because it's a long season—16 games and 17 weeks just to get to the playoffs," he says. "It's a contact sport and you're probably going to lose a guy at some point."

Even if you don't lose a guy, you might lose his burst. While we found no regular season pattern as runners racked up carries, check out the trend during playoff games over the last 10 years:

The stats are clear. After a running back passes 10 carries in a playoff game, his performance steadily declines. A long season of pounding seems to take effect in the playoffs, where a back lacks the fourth-quarter strength he might have owned in October.

3) It forces the defense to prepare for different styles.
It's difficult to quantify the importance of complementary backs. Jim Goodman, the Broncos' VP of Player Personnel is fond of "coming in with a guy who runs a 4.3 40 with fresh legs as a change of pace in the fourth quarter."

Even Johnson admits this can help, saying, "When we have someone who can come in, get on the edges, catch the ball, that's a plus. That's something else for the defense to worry about."

4) Time-shares save money.
We've already discussed how running backs might be overrated compared to offensive linemen. So, given the impact of the salary cap, does it make sense to pay top dollar for premier runner when you can buy two for less?

"If big-money deals are deemphasized, it's simply because of longevity," Fisher says. "They generally come in the guy's fourth or fifth year. But there's a philosophy out there that you get two, three, maybe four good years out of a back and then you've got to change. You wonder how many good years they have left."

So, if you're handing out a big contract, why give it to a super-back over, say, a left tackle or a defensive end (guys with longer shelf lives)? Then you can just throw leftover cash at two mid-level runners.

So which way should a team go? Rudi Johnson speaks for all running backs when he says, "Every team needs a dog, a guy who'll go get the yards for them. You've got to let the dog eat." But the Chiefs tried that with Larry Johnson two years ago, handing him the ball 416 times. Last year, he ended up missing eight games. "Larry said to me, 'Give me the damn ball,'" Peterson says, "Then we gave it to him 400 times and he said, 'I didn't mean quite that much.'" That's why, according to Peterson, the Chiefs drafted Jamal Charles. Even dogs need a nap.

But that doesn't mean you should altogether jettison a superstar. LaDainian Tomlinson is probably the best back in the league, but the Chargers would be silly to dump him. Instead they maximized his value by limiting his carries—he averaged only 19.7 attempts last year— and bolstering him with top-notch backup Michael Turner. With Turner now in Atlanta and Tomlinson facing a heavier burden this season, the Chargers might learn what everyone else is figuring out—two is greater than one.

It's hard to argue against a trend that's proved itself in five of the last six Super Bowls. When last years champs, the Giants, went from a Tiki Barber-based solo job to an (at times) four-man rotation, they had one thing on their side: history.