In today's pass-happy league littered with running-back-by-committee backfields, it's easy to forget that the NFL was once dominated by elite, workhorse running backs. Back when teams weren't afraid to feed their franchise tailbacks 400-plus touches, these athletes rose to the occasion time and again to put their teams on their backs and deliver some of the most valuable single-season performances of this century.

But of these performances, which were the most valuable? And how does one fairly compare running backs from different teams, going up against different sets of defenses, and in different seasons?

Well, here at numberFire we have a metric called our glossary.

Logically, one might therefore argue that the most valuable single-season performances by a running back are the ones in which the greatest NEP is accumulated.

Using our Rushing NEP metric I was able to rank the top five rushing performances by a tailback during the past 15 seasons. What follows are some truly remarkable feats of effectiveness and outright domination.

And to put these performances into perspective, the 50.78 Rushing NEP put up by number five on our list nearly matched the combined Rushing NEP of the top five leaders in rushing yards in 2014 -- DeMarco Murray, LeSean McCoy, Le'Veon Bell, Marshawn Lynch, and Matt Forte. Their combined Rushing NEP was just 53.79.