One could understand why Dallas Cowboys owner Jerry Jones didn't feel the need to get another running back following DeMarco Murray's departure this offseason. Dallas' offensive line is anchored by three first-round picks in Tyron Smith (LT), Travis Frederick (C) and Zack Martin (RG). La'El Collins (LG) is a first-round talent who is expected to compete for a starting job. While Jones may have been sipping a little too much of his own coolaid when he said Dallas' running game will be even better this season, there's no doubt that Cowboys rushers will have room to run.

But ESPN NFL Insider KC Joyner still believes that Dallas' running game will take a significant step back in 2015. As of now, Dallas is content entering the season with Joseph Randle, Darren McFadden and Lance Dunbar in the backfield.

"That sounds great in theory, but one of the reasons the Cowboys rushing game worked so well last season is Murray was able to post an 8.9 GBYPA on 160 good blocking rush attempts," Joyner wrote. "That volume of carries is highly important, as no other running back had more than 126 good blocking carries last year - a testament to Dallas' terrific offensive line. But the Cowboys still need a RB who can take advantage of available rushing lanes.

"Last season, Randle racked up a 12.6 GBYPA. That total would seem to indicate that he can keep up the production level, but it occurred on only 18 good blocking rush attempts. McFadden and Dunbar both fell drastically short of Murray's GBYPA total, with 6.9 and 6.6 totals, respectively.

"So unless Randle is able to replicate his GBYPA with a much higher carry volume - or McFadden/Dunbar improve drastically - this rushing attack will take a step backward in 2015."

Dallas' offense is a classic example of if the sum is equal to the whole of its parts. Will the Cowboys OL be good enough for any running back to produce or does Dallas need a top-tier runner to take full advantage of the quality blocking? How much does a specific running back truly contribute to winning?

All these questions will be answered for the Cowboys this season.