McCoy is the primary rusher on the Eagles, swallowing so many snaps as the top runner that even the No. 2 back in Philadelphia is not used the way he would be in other offenses. Still, the Eagles were not willing to part with either Brown or Polk.
"For us, once you get past, really, 40 [players], we're trying to get the best guys that can come on our team and maybe last for a long period of time as we try to build it," general manager Howie Roseman said. "Chris just did everything that [he] was asked for to make this football team."
The same could be said about Brown, the intriguing seventh-round pick out of Kansas State who was once a top high school recruit, barely played in college, and came to the Eagles unseasoned and brimming with potential. Polk was an undrafted rusher out of Washington who was productive in college, although beset by a shoulder injury that seemingly clouded his NFL prospects.
Brown displayed natural rushing skills throughout the summer that made him too exciting a prospect to part with while he developed raw parts of his skill set, such as blocking. And Polk, in Roseman's eyes, made a positive play "every time he touched the ball," showing a seasoned repertoire that includes a hard running style, blocking skills, and good hands out of the backfield. Roseman confirmed that the Eagles did not think he would clear waivers to make it to the practice squad if they had elected to cut him.
Polk ran for 1,488 yards and 12 touchdowns as a senior for the Huskies last season and would have been a valuable draft pick if not for whispers of a degenerative shoulder condition. He did not miss a single practice all summer, and there was never an issue with his shoulder during camp.
"I had my shoulder injury three years ago, and I never missed a practice in college or a game," Polk said. "I didn't really think it's an issue. I'm not holding it against [other teams]. They've been doing this longer than I've been born, so who am I to say. . . . Thank God I haven't had any shoulder pains. But even if it does hurt, I'm still going to play."
The questions regarding Brown during the summer were about acclimating to the NFL after only 13 college games at Tennessee and Kansas State. Running backs coach Ted Williams has been tutoring Brown, and Brown said he spent considerable time with assistant special teams coordinator Duce Staley, a former Eagles running back.
"I would say [I'm] understanding defenses better," Brown said when explaining the improvement in his game. "So, recognition of the defenses does carry a long way, but there's enough in that area I feel like I need to work on, too."
The potential of the two running backs could threaten the backup Lewis, although even Lewis earned praise this summer. McCoy continues to preach that no one knows how good Lewis is, and all three are stuck behind McCoy. That's the way the Eagles want it - the team is better when McCoy is on the field - but the Eagles made a decision to keep talent even where it's not a necessity. The next decision is determining how and when to use the rookies.
Practice squad additions. The Eagles officially added two players to the practice squad on Sunday: wide receiver B.J. Cunningham and defensive tackle Frank Trotter.
Cunningham was a sixth-round pick by the Miami Dolphins, while Trotter spent the summer with the Eagles. There is one spot left to be filled on the Eagles' eight-man practice unit.
Contact Zach Berman at email@example.com, or follow on Twitter @ZBerm.