More and more it seems Darren Sproles has become Chip Kelly's go-to-guy on offense.

The 5-foot-6 running back is much smaller than the prototypical back that Kelly covets, big shifty downhill runners like DeMarco Murray or Ryan Mathews. But somehow, Sproles is third on the Eagles in receptions and third in rushing attempts (after 15 rushes last week against the Bills).

He also has two punt-return touchdowns.

Kelly says there has not been a concerted effort to get Sproles more involved, but it's just the way the games have manifested themselves.

"He's one of those guys, kind of like a [Tyrann] Matheiu from Arizona, you throw those things out they are exceptions," Kelly said, referencing the Cardinals undersized, 5-foot-9 safety who has been a major impact player defensively. "I think their competitiveness and ability to make plays outweighs any concerns from that standpoint."

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Mathieu has 84 tackles and four interceptions this season and has been mentioned among candidates for NFL Defensive Player of the Year for a few weeks now. And like Sproles, he has shaken off the shackles of being called 'undersized,' to become one of the NFL's best defenders.

"He has a nose for the football, he rises to all challenges," Kelly said. "He is a little smaller but he did great job on Jimmy Graham (the Seahawks 6-foot-7 tight end)."

So just as Bruce Arians will undoubtedly be spending ample time worrying about Sproles, Kelly will be worrying about Mathieu.

"You just have to have someone assigned to him, know where he is, look at the coverage and see where he is coming," Kelly said of the oft-blitzing safety.