When the Eagles break camp Tuesday at Lehigh University and pack the trucks for the last trip down the Northeast Extension, the remainder of preseason training moves to the figurative and almost literal shadow cast by Lincoln Financial Field.

This is when the pace of preparation quickens and the decisions that will shape the team become more difficult. It's a short ride from here to the Sept. 12 opener, which is fine for the starters and the players with solid spots on the team. Further delay can only bring bad things for them. But it's a brutally tense time for those trying to carve a niche for themselves and secure a place on the 53-man roster before it lifts from the ground and leaves the unlucky peering into the sky at the departing dream.

They study the depth chart and play the numbers game. How many running backs will Andy Reid keep? How many tight ends? Linebackers? How do the injuries to Antoine Harris and Quintin Demps affect the defensive backfield? Will Todd Herremans and Jamaal Jackson be able to play at the start of the season? All of these combinations are like tumblers in a lock, one affecting the next until everything falls into place.

So, they live on the bubble, guys like Austin Howard and Cornelius Ingram. Jamar Chaney and Charles Scott. Not on the team exactly, but not off it yet, either, and the days roll by faster and faster, marking off their final chances to make that one play, that one impression that matters.

"You just try to be remembered," said Chad Hall, a combination running back/receiver/returner getting a long look in these final weeks. "You try to stand out every practice."

Hall's ticket to the roster probably will have to pass through the special-teams gate. It is his good fortune that DeSean Jackson, a Pro Bowl punt returner last season, has probably become too valuable to the offense for that assignment. Ellis Hobbs is listed as the top kickoff-return man, but someone else has to be back there as well and both Macho Harris and Demps have had injury issues. There is a spot developing for a player who can perform both functions, and if he can operate as an occasional slot receiver or take a handoff in the backfield now and then, so much the better.

That is what Hall hopes, anyway. He is 5-foot-8 and Friday's exhibition against Jacksonville was his first formal football game in 21/2 years, but he knows he has a shot at playing in the National Football League. That's all he asked for.

"They're giving me an opportunity to see what I can do," Hall said. "I'm thankful for that, thankful to be in this situation. I'm working my butt off trying to do every extra thing. They gave me this opportunity starting in March and I'm trying not to let them down. I'm looking for a way to make this team better."

Hall returned two punts and three kickoffs on Friday. He played one series at receiver, catching three passes, including a 57-yard catch-and-run. He played one series at running back, getting two carries, including one for a 22-yard gain.

"I thought he had a productive day," Reid said. "He was a secure catcher of punts, and it looked like he made good decisions in terms of when to let the ball go and when to fair-catch it. He also had a nice play from the receiver position and he ran the ball well."

Hall is officially listed as a wide receiver, but his playing background is all about his versatility. Hall was the Mountain West Conference's offensive player of the year in 2007 as a senior at the Air Force Academy. He compiled 2,683 all-purpose yards, the only Division I player to lead his team in rushing, receiving, and all-purpose yards.

After graduating with the rank of second lieutenant, Hall was stationed at Hill Air Force Base near Salt Lake City as the assistant officer in charge of maintenance for a squadron of F-16s. After a full 10- to 12-hour shift on the flight line, he would make the 90-minute round-trip drive to the University of Utah to work out at the football training facility.

"Lt. Hall informed me of his goals of joining the NFL the day I met him," Chief Master Sgt. Carl Juntunen, a coworker at Hill, said in the official academy news release announcing Hall's signing. "So when we found out he was selected, I was not surprised."

Everything about the success of a small player from a small school, so long away from the game, might be surprising, but not necessarily in Hall's case. He was impressive during a "pro day" tryout at Utah in March, was invited to Philadelphia to work out for the Eagles, and was quickly offered a contract. With that in hand, he was able to apply for a switch from active status to reserve status with the Air Force, a change that doubles his three-year commitment but also allows him to play football.

"It was good to be back in a game," Hall said Friday.

Now there is only the wait to find out if he will remain in the games for the Eagles. Hall said he doesn't really pick over the roster and attempt to figure out all the mathematics that will eventually add up to 53. He just knows he has a chance.

"That's way over my head," he said, "All I can look at or care about or control is what I do. The numbers game is part of the business. I learned that early when people are cut after day one, or brought in and cut after one practice. I know it's a different world here and they're going to make decisions. I can only control me and do the best I can."

For the lucky ones, that even turns out to be enough.