In a season whose stench surpasses that of the Augean stables, there have been only a few bright spots. Since it would take even Hercules more than single day to clean up this team, let's instead focus on one of the best reasons to continue to watch the Vikings every week: Adrian Peterson.
After playing in 100 games, AD is at a good point for evaluation. He's gained 9846 yards on the ground, which for the mathematically challenged is an average of 98.46 YD/GM. This total through the first 100 games exceeds those of all running backs not named Eric Dickerson (10,818) or Jim Brown (10,403), with Barry Sanders (for perspective) close behind at 9746.
Currently, this total is good for #29 on the all-time list. Of active running backs, only Steven Jackson (10,390, #25) is ahead of him. Although 2013 has been a disappointing for him and the Falcons, he is still likely to gain an additional 60-200 yards this season, which would see him end the year sliding ahead of Tiki Barber (10,449) to #23, but behind Thomas Jones (10,591, #22). No active back is close enough in the rear-view mirror to be a near-term threat to AD's ranking, so now we can start to speculate on his future performance and what it will mean for his legacy.
First, let's focus on the rest of this season. Barring unforeseen circumstances, it's pretty likely that AD will eclipse 10K career rushing yards this season. In fact, since the Bears are ranked dead last in stopping the run, giving up an average of over 146 YD/Gm, it would not be surprising for that to happen this Sunday. Unfortunately, it gets harder after that.
While the Eagles are #20 against the run, surrendering almost 118 YD/GM, the Ravens (#10, 103), Bengals (#9, 102), and Lions (#4, 87) are much more challenging. For the sake of speculation, let's project AD to gain 150, 100, 120, 100, and 80 yards in the games remaining. That's a total of 550 yards, which would bring him up to 10,396. That would be good for #25 all-time, assuming Steven Jackson is able to gain at least 7 more yards this year.
The next two years at TCF Bank Stadium are where things start to get really interesting. How will playing home games outdoors affect AD's production? On the one hand, the grass may not offer as good a purchase to play on as an artificial surface; yet on the other, inclement weather might well see an increase in running opportunities. For now, let's say it's a wash and continue to use the historic 98.5 YD/GM average for this period.
(Two side notes: One, despite the salary implications pointed out by MarkSP18 and others, I believe Adrian will continue to be a Viking for the next two seasons at least. The Wilfs have to give the fans a reason to brave the elements, and with many beloved veterans leaving the team and the QB position likely to have growing pains, AD will certainly be the biggest draw available. Two, I do think it is reasonable to project AD's near-term future performance as being similar to his recent past. Dr. Andrews said his knees after surgery looked remarkably young for as much use as he'd given them, and we all know how dedicated AD is to his training and conditioning.)
Projecting 1500 yards per season for the next two years would leave AD looking at 13,396, good enough to leapfrog Eric Dickerson (13,259) into 7th place.
But then what? When the new stadium opens in 2016, will Adrian Peterson still be a Viking? That's a hard question. Undoubtedly he'll still be tremendously popular, but is it realistic to spend $14.75M on a 31 year old running back, even if he's a lock for the HOF? That year, his guaranteed money and prorated signing bonus will have been completely paid out, and there would be no cap hit to cut or trade him. I see four possible scenarios: pay his existing contract (20% likely); trade him (20%; remember that the new team would have to assume or renegotiate his contract); cut him (20%), or renegotiate a new contract (40%). That contract is going to be a problem no matter what, but it would not be crazy to see the Vikings offer a new 3-5 year contract with some guaranteed money (and perhaps escalators) in exchange for tearing up the last two years of this one.
Where he plays, and whom he plays for, may affect his yardage, as may the effects of age and abuse. It would be reasonable to expect a decline to say 3/4 of his historical average at this point (call it 1200 YD/YR). However, keep in mind that he clearly has his sights set on proving he's the best. With our projections of AD's first nine seasons so far, he would still be 1873 yards shy of matching Barry Sanders (15,269) through his ten seasons. So either he exceeds these projections, or he has a hell of a year to catch up. Or he takes another year to climb past #3 all-time.
If he is still playing in 2017 and later, #2 Walter Payton is almost another 1500 yards past Barry Sanders at 16,726, and the crown is currently worn by Emmitt Smith, who took 15 seasons to gain 18,335 yards on the ground. If AD can keep playing at a high level, it will probably take until 2019 or beyond before he would become the GOAT. Can he do it? Will he?