PHILADELPHIA — When Coach Chip Kelly sent David Ball a text message last week to ask him if he was free to join the Eagles at their training camp, Ball packed his gear and took an immediate sabbatical from his day job as a high school football coach in Vermont.

“It doesn’t matter to me whether this is three days, three weeks, three months or three years,” Ball said Wednesday afternoon between practice sessions at the team’s training camp. “This is my last stop, because this is where I’ve always wanted it to end.”

Training camps are speckled with players like Ball: the unsung, the overshadowed, the disregarded. Ball’s most recent stop in professional football came two years ago with the Erie Explosion of the Southern Indoor Football League, where he plied his trade at wide receiver on a concrete surface that was camouflaged by something that vaguely resembled miniature-golf turf.

“It was a tough way to play,” he said.

While most training camp invitees are casualties of preseason cuts, Ball, 29, has something unusual working in his favor: a deep connection to Kelly, the Eagles’ first-year coach. Before Kelly was celebrated as the architect of Oregon’s supercharged system, he was the offensive coordinator at New Hampshire, where his most dynamic playmaker was an undersized receiver named David Ball.