Otis Smith and Mike Caldwell are the two rarest birds on the Eagles' coaching staff. In fact, they are a rare breed throughout the NFL.

Hired this off-season by coach Andy Reid, Smith and Caldwell are the only two members of the team's 21-man coaching staff who have also played in the NFL. The fact that the Eagles have so few former NFL players on their coaching staff is not an unusual league trend, and there's good reason for it.

"It's tough work," former Eagles linebacker Ike Reese said during the Eagles' rookie camp last week, which is set to resume with a few selected veterans in attendance today. Reese is now a sports talk-show host at WIP-AM (610).

"You're talking about logging a lot of hours, especially when you're starting at an entry level. You're paying your dues."

Smith, hired as an assistant secondary coach in late January, had the passion for coaching while he was still playing. The former cornerback, whose career started when he debuted with the Eagles as an undrafted free agent in 1991 and ended two seasons after he won a Super Bowl with the New England Patriots in 2002, said the late Andre Waters provided the first bit of inspiration.

"He taught me how this game works," Smith said. "I lived with Andre for a little bit. He used to say, 'You have to be a student of the game first and then when you become a student, you have to be a coach of the game.' What I did, I was a coach of the game when I was still playing. Whenever young guys came into a system, I brought them along and tried to make them a better player."

Smith, 42, played 13 seasons in the NFL and made enough money that he doesn't have to be an assistant coach. But he said Waters and two other former Eagles - Wes Hopkins and Reggie White - injected him with the same passion that they had for the game as players, and it remains with him as a coach.

Waters committed suicide in 2006, and a pathologist later determined that brain damage incurred from the jarring hits he delivered during his NFL career may have led to depression. Waters aspired to be an NFL coach and, like Smith, he was willing to start at an entry-level position.

Smith and Waters were both undrafted players, and that's the kind of player the Eagles' assistant secondary coach hopes to help in his new NFL role.

"I want to take players that are green or came from a small school but have potential and turn them into good NFL players," Smith said. "That's what is very gratifying."

Unlike Smith, Caldwell didn't envision himself becoming an NFL coach during his career, which spanned 11 seasons, including four with the Eagles and three with Reid.

"When I was a player, I said I'd never do it," Caldwell said. "Then I got away from the game for a while, and I was actually coach of my daughter's basketball team in Georgia."

That work with his daughter's 8-and-under girls' team inspired Caldwell to give coaching a try, and when Reid called to ask him if he wanted to work on an intern basis during training camp last summer, the former linebacker jumped at the opportunity.

"I kept hearing from guys that it was going to be this, that and the other, but I had a blast," Caldwell said.

Forced to reconfigure his staff because of John Harbaugh's departure to become the Baltimore Ravens' head coach, Reid made a number of changes, including adding Caldwell as the defensive quality control coach, which means he'll be breaking down film on opposing teams. It's the lowest rung on the NFL coaching ladder, but Caldwell has no complaints.

"I'm trying to be a sponge right now," Caldwell said, "and absorb as much as I can."

Contact staff writer Bob Brookover at 215-854-2577 or bbrookover@phillynews.com.