One current common cry among NFL fans is "Pay the man!" We hear this most often right now about Chicago's Matt Forte, but we're soon going to be hearing it about Arian Foster and Ray Rice as well. All three of these young stars see their contracts end after this season, and there's been a lot of debate about how much money their teams should offer to try to prevent them from hitting free agency.
Paying running backs is a difficult proposition. Star running backs generally have shorter careers than stars at any other NFL position, and there always seems to be the danger that a running back will unexpectedly flatline. Often this happens after a season or two of massive overwork (Shaun Alexander, Larry Johnson), but other times it happens seemingly without warning (Chris Johnson this year being the scariest example, since he had just signed a huge-money contract). In addition, plenty of teams have gotten strong value out of running backs they found on the scrap heap -- undrafted free agents like Foster, BenJarvus Green-Ellis and LeGarrette Blount. Where those backs were found, there are others waiting.
I've generally been a proponent of not paying big money to running backs, arguing that teams should constantly churn through younger backs while dedicating money to other positions, particularly offensive linemen -- who often have more impact on rushing success than the running back himself.
However, there are exceptions. There are certain running backs who truly are significantly better than their counterparts, enough to overcome the basic concept of "running backs are fungible." LaDainian Tomlinson at his peak would qualify, as would Adrian Peterson today. If you've got a back like that, and you can get him in his mid-20s, it may actually be worth paying that big salary.