Inside Slant: History working against Adrian Peterson, other RBs

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Two of the NFL's best running backs spent last week hollering into the wind. Jamaal Charles, 28, predicted that technology and new training methods will push him and other runners into mid-30s productivity. Almost on cue, Adrian Peterson, 30, campaigned publicly for an upgraded contract.

Decades of history are stacked squarely against them, and it's difficult to imagine the lifespan of their position changing as long as NFL defenders can pummel them at will. The average cutoff for peak production of late is 27 years old, as we noted last year, and elite status after 30 -- as Peterson's request would imply -- is rare.

In the NFL's 95-year history, there have been 46 instances of a 1,000-yard season by a running back who is at least 30 years old. Only four times has it happened for one older than 32, and not once since 1984.

A 1,000-yard season is not the sole marker of a productive season, of course, and there are always exceptions and outliers. As the first chart shows, the New York Giants got 1,860 yards out of 30-year-old Tiki Barber in 2005. (Barber followed with 1,662 yards at 31 before retiring.) The second chart notes that strongman John Riggins exceeded 1,200 yards twice after age 33.

This context seems relevant amid public assumptions of a monster season for a running back of Peterson's age. It's true that Peterson will have fresh legs after missing 15 games last season, and those who know him well say he is highly motivated by the scorn he received for his child abuse case. But justifying significant guarantees to his contract for 2016 and possibly beyond, starting when he is 31, would bypass decades of history.

Peterson has proved the exception before, most notably after totaling 2,097 yards a year after tearing two ligaments in his left knee. But consider the case of Barber, who produced his best two seasons at ages 30 and 31. In his first five years, Barber took 629 carries -- less than half of Peterson's workload (1,406 carries) over the same time period (629 versus 1,406). Even Riggins, a workhorse who had nearly 3,000 carries in his career, took about 35 percent fewer carries in that crucial early period. Peterson has more early career mileage on his body than many of the names on this list.

I'm all for NFL players getting as much guaranteed money in their contracts as they can, but this context is what the Vikings and most other teams would use to consider Peterson's request. In essence, he is asking to cast aside well-defined trends and assume he'll provide the exception.

Already, Peterson's contract is an outlier. His $12.75 million base salary is all but guaranteed, considering the Vikings have made clear they want him to return under those terms. Guess how many 30-plus running backs have any true guarantees in their deals? Two, Frank Gore and DeAngelo Williams, for a total of $7.78 million, per ESPN Stats & Information's contract database.

Given the relatively paltry pay, it's no surprise Charles suggested last week that running backs can reverse or at least fight off history. As he nears the (typical) running back's twilight, Charles said he wants to play into his mid-30s and implied he had learned techniques to avoid physical pounding.

"Football is changing, sports are just changing," he told the Chiefs' website. "You can see basketball, like Kobe Bryant, he is still playing at 36. You see Tim Duncan. I think back in the days you couldn't play for long because there were a lot of people that didn't know the fundamentals of hitting, running people over. That's not my form."

Short of receiving quarterback-like protection, it's difficult to imagine a running back truly preserving his body via technique. Few teams are interested in running backs who avoid contact.

What they do prefer is squeezing out the final years of a running back's career at value.

In addition to the Vikings, four teams are counting on primary runners who will be at least 30 years old by the end of the season: the Indianapolis Colts (Frank Gore), Baltimore Ravens (Justin Forsett), Chicago Bears (Matt Forte) and New York Giants (Rashad Jennings). The Buffalo Bills and Pittsburgh Steelers, meanwhile, plan to use Fred Jackson (34) and DeAngelo Williams (32) in their rotations, respectively. The average 2015 compensation for those six players is $3.75 million.

Could Adrian Peterson produce an elite season in his 30s? Of course. Can Jamaal Charles play another six seasons? Perhaps. Robert Kennedy told us to dream of things that never were and ask "Why not?" In this case, at least, the answer seems clear.