As the NFL continues to shift into becoming an even more pass-happy league, running backs continue to adjust to this new norm through greater incorporation into the passing game.

A few running backs have established their reputations as this type of specialist over the course of their careers -- think Darren Sproles, Pierre Thomas and Shane Vereen -- but are there any backs out there who should be seeing a little more work through the air out of the backfield?

To find out, we can look at numberFire's Net Expected Points (NEP) metric, which helps us measure player efficiency by quantifying the theoretical points they add to their team's score based on their performance above or below expectation. Add up all of the plays they're involved in, and you get Net Expected Points.

You can read more about NEP in our glossary.

Receiving is far more efficient than rushing due to its nature of the ball traveling through the air, thus netting larger chunks of yards on average in a single play. Still, running backs are far less likely than wide receivers to achieve a high Reception NEP (NEP on catches only) on a per-target basis because receptions by running backs often result in less impactful plays.

The numbers bear this out. The table below shows running back production versus wide receiver production per target and on a Success Rate basis from 2014. Success Rate, for those unaware, is the percentage of positive plays in terms of NEP. Put simply, it’s still harder for running backs to be as efficient as wideouts on a per-target basis.

Who Should be Getting the Rock More?

So, based on our data from last year, which backs should be getting more looks in the passing game?

To determine this, I had to establish some common-sense parameters to define a running back as under-utilized while taking into account that, at some point, the number of targets a running back receives can be too small to draw any conclusions about his true efficiency on the field.

Thus, qualifying backs for this analysis include those who received between 20 and 50 targets in 2014 while achieving a Reception NEP per target of at least 0.15 points over the league average for running backs, and at least a 70% Reception Success Rate (the percentage of receptions positively contributing to a player's Reception NEP). These are somewhat arbitrary parameters, but they at least give us an idea of which players were well above average through the air out of the backfield.

So who should be getting the ball more out in space? Some of the answers might surprise you.

The two candidates included in this list that probably best met the eye test in 2014 are Ahmad Bradshaw and C.J. Anderson. Prior to Week 11, Bradshaw was on a receiving tear last season with six touchdown receptions. But then an injury sidelined him for the rest of the season.

And C.J. Anderson was only named the starting running back in Denver after Montee Ball and Ronnie Hillman both suffered injuries. Needless to say, given a full season’s worth of playing time, Bradshaw and Anderson would’ve been excluded from this analysis.

So let's dig deeper into some of the other names on the list.

Lance Dunbar, Dallas Cowboys

Everyone knows that the Cowboys rode DeMarco Murray into the playoffs last year, but Lance Dunbar did grown man’s work when given the opportunity through the air in 2014. Dunbar’s 2014 qualified as the sixth-best season since 2000 in terms of Reception NEP per target among all running backs who received at least 20 targets in a season.

His Reception NEP per target bested the average wide receiver mark in 2014 by 0.20 NEP, and his Success Rate approached that of the average Success Rate for wide receivers in the league -- again, an extremely difficult task given that running backs typically catch the ball much closer to the line of scrimmage. If Jason Garrett and Scott Linehan know what's good for them, they’ll find a way to get Dunbar the ball out in space more frequently in 2015.

Damien Williams, Miami Dolphins

Damien Williams has a legitimate chance to carve out a role on the Miami Dolphins on passing downs. Why? Well first of all, he was very effective on a per-touch basis. Secondly, as good as Williams was through the air on a per target basis, Lamar Miller was as bad. Amassing a 0.22 Reception NEP per target, Miller far underperformed the league average for running backs. Giving Williams more third-down passing game work so Miller can continue handling the rushing load would be a smart move by Dolphins offensive staff in 2015.

Charles Sims, Tampa Bay Buccaneers

At one point last season, Charles Sims had garnered a fair amount of hype for potentially being the guy to replace Doug Martin in Tampa Bay, whose skills seemed to drop like a rock from his rookie season in 2012. But when Sims got the chance to tote the rock on the ground, he was incredibly ineffective, garnering a -0.24 Rushing NEP per rush, one of the worst per-rush averages in the league.

So you’d be forgiven for thinking Sims did nothing positive in 2014, however, his work through the air was actually pretty impressive. By achieving a 0.57 Reception NEP per target in 2014, he proved to be far and above the best receiving back on his team with both Martin (a miserable 0.02 Reception NEP per target) and Bobby Rainey (0.24 Reception NEP per target) performing worse than the league average for running backs.

Toby Gerhart, Jacksonville Jaguars

If you would have told me Toby Gerhart was good for anything in 2014 besides providing an overhyped pre-fantasy-draft buzz, I would’ve broken out my "bridge to sell you" sales pitch on the spot. Thankfully, it didn’t come to that point, because everyone on planet earth thought Gerhart was awful last year.

But Gerhart was actually pretty productive through the air last year with the limited opportunities he received, achieving a 0.49 Reception NEP per target and a 75% Success Rate. Not only that, but his running back counterpart on the Jaguars, Denard Robinson, was wildly ineffective through the air, putting up a mere 0.13 Reception NEP per target, well below the league average. It wouldn’t solve their overall ground game problems, but the Jags would do themselves a solid by utilizing Shoelace in the passing game a lot less frequently, and siphoning some or most of his targets to Gerhart.

Bryce Brown, Buffalo Bills

Finally, we have Bryce Brown. Forever stuck in a running back platoon, Brown was really good through the air last year when given the chance.

Stuck behind Lesean Mccoy in 2012 and 2013 and Fred Jackson and C.J. Spiller in 2014, Brown is destined for another season behind Jackson and, after a one-year hiatus, McCoy once again.

Neither McCoy nor Jackson have come close to matching Brown’s insanely high 93.75% Success Rate from 2014 in a single season. And Jackson, while receiving a large amount of targets in the Buffalo offense, hasn’t been especially efficient through the air since his 2011 campaign. In fact, that was the only season in Jackson’s career in which has matched Brown’s 2014 receiving efficiency on a per target basis, by achieving a 0.48 Reception NEP per target. In 2012 and 2013, Jackson slightly underperformed the league average Reception NEP on a per target basis.

McCoy’s first year in Chip Kelly’s system (2013) helped him produce a very efficient 0.49 Reception NEP per target, but in 2014, that cratered to an abysmally ineffective 0.04 mark. Between the 2010 and 2012 seasons, McCoy’s Reception NEP per target stayed between 0.30 and 0.33, right around the league average. Shady’s receiving effectiveness in 2015 is likely to be somewhere close to his average pre-Chip Kelly introduction, thus warranting Brown some extra work through the air. But if last season was any indication about the evolution of Shady’s game, then Brown definitely deserves more targets out in space.