Once the 2015 NFL season finally rolls around, there's really no question who is going to see the lion's share of carries for Philadelphia Eagles head coach Chip Kelly's offense. Kelly signed last season's leading rusher in the league DeMarco Murray away from the rival Cowboys and added former first-round pick Ryan Mathews for good, downhill running, measure. The diminutive, but tough and versatile, Darren Sproles remains in place as a dynamic offensive jack-of-all-trades, just as likely to impact the game split out wide or in the return game as he is by seeing a touch out of the backfield. In short, barring any catastrophic injuries, the top of the Eagles running back depth chart is about set as set can be. But what about beyond the top three options?

The team recently waived Matthew Tucker, who had a good combination of size and athleticism and seemed like a Kelly favorite, after he injured himself training for the season. With Tucker out of commission and Chris Polk given his walking papers this offseason, that leaves few established back-up options for Kelly. Or so it would seem.

Despite the losses of Tucker and Polk, Zach Berman of The Philadelphia Inquirer reports that the Eagles could still keep four running backs, as they're "real comfortable" with former Kelly Oregon protégé Kenjon Barner and are "intrigued" by rookie free agent Raheem Mostert.

Considering the team released tight end James Casey and seem to have a ready replacement for Casey's special teams and third tight end duties in Trey Burton, they may only carry three tight ends after going heavy at the position for the first two years of Kelly's tenure. In doing so, they'd free up a roster spot for a potential extra running back, meaning the well-known Barner and the intriguing Mostert - along with recent addition, former Villanova back Kevin Monangai - may be battling one another for a spot on the 53-man Eagles roster.

Barner, 25, was a sixth-round pick by the Carolina Panthers in the 2013 NFL Draft. He appeared in just eight games for the Panthers that season, managing just six carries for seven yards. Barner was acquired by Kelly and Co. in August of last year in exchange for a conditional seventh-round pick.

While Barner has yet to make his make at the NFL level, there's no denying he has ample natural talent and if there's any coach who can coax it out of him, it's Kelly. Under Kelly at Oregon, Barner placed in 49 games and ran for 3,623 yards, averaging 6.2 yards per carry. He scored 41 rushing touchdowns, including 21 his senior year. He also contributed on special teams, returning 61 kickoffs for 1,371 yards and one touchdown and 26 punts for 263 yards and one touchdown.

"Kenjon will hopefully bring some depth to both our running back and return positions. He's obviously a guy I know really well from Oregon, where he had a very productive career," Kelly said at the time of Barner's addition. "He has a lot of speed, explosiveness and had a knack for making some really big plays. But our plan with him right now is get him in Philadelphia as soon as we can and plug him in at running back and returner and let him compete."

As for Mostert, the former Purdue running back is all about speed. This is what NFL.com's Bryan Fischer said about Mostert back in June 2014, when he ranked Mostert the fastest player in college football.

"No speed in the Big Ten? Think again. The Purdue running back qualified for NCAA Outdoor Track and Field Championships in the 100 meters, 200 meters and 4×100-meter relay this year. He hasn't made a huge impact on the field for the Boilermakers, but is an ace return man."

Mostert made his biggest impact from the backfield his senior season at Purdue, managing 529 rushing yards on 93 carries. He added 116 receiving yards on 18 receptions.

From the sounds of things and considering Philly's ample running back depth, if Barner or Mostert or Monangai are going to separate themselves and/or make a serious run at the roster, it will likely have to come via special teams. If Murray, Matthews and Sproles stay healthy this season, it may not matter from a highlight reel standpoint, but if Barner or Mostert are able to make their mark in the third phase, they could potentially find themselves a key component of Dave Fipp's unit.

And considering Murray and Mathews both have lengthy injury histories; it's certainly not outside the realm of possibility that the fourth running back will see some time on the field next season.

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