The Eagles traded Bryce Brown to the Bills for a 2015 conditional fourth-round draft pick, parting with the young and promising running back who had ultimately become expendable.

"They had been on him for a while," Eagles coach Chip Kelly said of the Bills. "We probably fielded a lot of offers from them in terms of what they wanted, because we knew what they wanted and how much they wanted Bryce. It's just, we kind of had a logjam, so to speak, at running back."

The 2015 fourth-round pick the Bills dealt to the Eagles, which Buffalo received from the 49ers on Friday in exchange for wide receiver Stevie Johnson, could become a 2016 third-rounder or a 2016 fourth-rounder. It will depend on Johnson's production in 2014.

The Eagles and Bills also swapped seventh-round picks in Saturday's final day of the NFL draft. The Eagles moved up from the 237th overall pick to the 224th and used the selection on Wisconsin nose tackle Beau Allen.

There had been speculation that the Eagles had outside linebacker Brandon Graham and possibly defensive end Vinny Curry on the trading block during the draft. But neither was dealt.

Brown, who turns 23 next week, told Buffalo-area reporters that he was surprised by the move but looking forward to this new phase of his career.

He was chosen by the Eagles in the seventh round of the 2012 draft. He impressed as a rookie when he filled in for the injured LeSean McCoy, rushing for 169 and 178 yards in back-to-back games, but he also had ball-security issues.

He came back in 2013 determined to be more reliable and didn't fumble once in 75 carries. But Brown didn't have the same production when he got the ball. Aside from the Bears game, in which he ran for 115 yards on nine carries, Brown rushed for 199 yards on 66 totes (3.0 avg.) in the other 15 games.

By the end of the season, Chris Polk was playing as many snaps. The Eagles added Darren Sproles in the offseason. With McCoy, arguably the best running back in the NFL; Polk; Sproles; and Matthew Tucker still on the roster, the Eagles, to no great surprise, dealt Brown.

We're "really excited about Chris Polk and how he's come along," Kelly said. "Chris is an outstanding special-teams player for us. . . . I really think Chris is a hundred percent healthy and is vying for time there. We really like Tucker."

Polk (2012) and Tucker (2013) were both signed as undrafted rookies.

Brown was a couple of dozen picks away from not being drafted out of Kansas State. But the Eagles took a chance on him despite a rocky collegiate career in which he left two programs.

Big (6-foot, 223 pounds) and fast (he was once clocked running a 4.38-second 40-yard dash), Brown had a rare combination. But he often went outside on carries, especially in Kelly's offense, when running north to south would have sufficed.

Kelly, asked if Brown's lack of experience held him back in the pros, noted that the lack of wear and tear on the running back gave him a "big upside." It was one reason the Eagles held out from trading him despite the Bills' and other teams' persistence.

"That is always the dilemma," Kelly said. "Are we going to let him go too soon? Where is he in the whole thing? But, you know, it also was difficult because LeSean's only 25. And Chris is young. There is only one ball."