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Morry Gash/Associated Press

The truth of the modern NFL is this: Running backs don't generally mean what they used to.

The main men in most offenses in the previous millennium, backs must now do more to keep their esteemed positions—for the most part. Largely gone are the days of the one-trick pony—the power back who gets 300 carries a season to extend drives or the pure sprinter who gains 2,000 yards in a campaign.

For the most part, modern running backs must be some combination of first-down smashers, second-down pass-catchers and third-down blockers—and they'll most likely be doing so in some sort of committee.

The numbers bear this out. A recent study from FiveThirtyEight indicated the top 16 running backs in 2017 will earn less than players at any other skill position on offense or defense and that the average NFL back will make about half of what he did in 2000, relative to other positions.

This jibes with the notion that the NFL has turned into a quarterback's league, as does the distribution of passes to runs over the last 50 years. In 1970, the first season of the AFL-NFL merger, teams averaged 439.7 rushing attempts and 376.8 passing attempts. In 2016, they averaged 571.7 passing attempts to 416.3 rushing attempts. It's been a gradual shift, but it's drastic in the context of time.

So, to make the running game work in today's league, a back has to be efficient in everything he does, and he must do more things. The best backfields are manifestations of this understanding—that yes, it can still be about one transcendent back in rare instances, but far more often, multiple and different types of players will be sharing the load.

And with that understanding, we rank the NFL's backfields from worst to best. These rankings are less about the guy at the top of the rotation unless the top man defines the offense. It's more about how teams distribute carries and touches to the best advantage for their offensive philosophies.

Because in this era, that's what counts. And in 2017, it's the potential of one veteran switching teams that could decide the NFL's best backfield. If Adrian Peterson still has enough left in the tank, he could put the Saints' offense over the top--and over the backfields of the Titans and Falcons.