Earl Wolff played safety on the top defensive unit on Wednesday, adding a new wrinkle to the fiercest competition for a starting spot on the Eagles roster. Wolff had been behind veteran Nate Allen as the second safety next to Malcolm Jenkins at the start of training camp.

"I'm not going to look at it as I'm running with the ones," Wolff said. "I'm looking at it as I'm taking advantage of every opportunity I have with the ones, and I feel like I did a pretty good job today."

The depth chart is not firm in late July, and there will be much time for the coaches to choose a starter. Allen has the experience, but Wolff has shown improvement in his second training camp.

"Nate is a veteran, he knows what he's doing, he's in the right place at the right time," Jenkins said. "Earl is a young player who's got a lot of talent. Everything he's done so far has been off of raw talent and athleticism. He just has to learn the game."

Cooper sits again

Wide receiver Riley Cooper missed his second consecutive day of practice with a foot injury that does not appear to be serious.

Thursday marks one year since the video was released showing Cooper using a racial slur at a concert. Cooper has since established himself as a starter. Coach Chip Kelly said he values Cooper's size and how he uses his body to get open.

"That's one of Riley's strengths is his ability to get off that stuff," Kelly said. "No one's going to get off clean and just be running down the field with no one around him for 4 or 5 yards. When the ball is up, you have to be able to go get it. Having a 6-4 guy that's 230 pounds, it helps."

Running back Chris Polk missed practice with a hamstring injury, and center Julian Vandervelde sat out with a back injury. Defensive lineman Bennie Logan returned to practice after missing time with a sore hamstring.

Fathers and sons

Among the Eagles' ball boys is La Salle High quarterback Kyle Shurmur, who has committed to play at Vanderbilt. Shurmur is the son of Eagles offensive coordinator Pat Shurmur. The sons of offensive line coach Jeff Stoutland, quarterbacks coach Bill Musgrave, and tight ends coach Ted Williams also worked at Eagles camp.

"I think it's positive that fathers and sons can be around in the work environment," Kelly said. "They're just ball boys running around. If we ever need their arm somewhere, we get them. . . . I just think it's positive if we have a chance to have a lot of coaches with their kids at practice."