But from here on out, the games count. So when the Eagles open their second season with Kelly at the helm Sunday against the Jaguars, it will be the first opportunity to truly see how the versatile Sproles impacts the already high-powered offense.
Thus far, nine carries for 44 yards and three catches for 17 yards are all Philadelphia fans and the rest of the league have been privy to observe of Sproles in an Eagles uniform.
"They ain't seen nothing yet," he said after practice yesterday.
Sproles obviously wouldn't offer particulars on how the Eagles plan to use him, but did say, "They're going to see me in space, pretty much. That's what it's going to be."
Entering his 10th season in the league, Sproles, 31, has proved himself as an elite pass catcher out of the backfield. His 375 receptions and 3,371 receiving yards since 2007 lead all NFL running backs. As do his 27 receiving touchdowns, 11 more than Reggie Bush, the back owning the next-highest total in that span.
Throughout the last five regular seasons, Sproles has more catches (336) than carries (331), though the Eagles have maintained all spring and summer that he is indeed a running back.
"He can do a lot," Kelly said. "We're excited about him. Again, I've said he's a really talented runner and you'll see him carrying the football, and he's obviously a weapon coming out of the backfield. So you'll see a lot more out of him."
Sproles, who was acquired via trade from the Saints in March, is genuinely eager for the start of his first regular season in Philadelphia.
"We haven't shown anything yet," he said. "I'm actually excited about it."
The Eagles' newest running back said he hopes to keep McCoy fresh, adding, "If you're going into the fourth quarter fresh, the defense is going to have a little trouble I think." Behind McCoy and Sproles is third-year back Chris Polk, who made the 53-man roster despite missing almost all of training camp and each of the four preseason games with a hamstring injury.
Polk practiced yesterday and said afterward he was "feeling really good." The plan, he said, is for him to play Sunday, but he noted he's "got to play it smart."
"It's a long season," he said. "I don't want to be here 1 week, aggravate it and be gone the rest of the season. We'll for sure know [today], see how it goes."
At the beginning of yesterday's practice, Polk was seen lying on his back stretching out with the assistance of a trainer. He explained afterward he just wanted to make sure he was completely warmed up before he started sprinting. Because he is coming off an injury, it takes him a bit longer to warm up. He also said "the only downfall I would have from sitting out so much, especially for our offense, I definitely would say [is] stamina. Because in order to be in football shape, you have to play football. But that will come back to me. That will come back to me soon."
Because of his inactivity, Polk had to sweat out the Eagles' cut day last week before learning he made the active roster over Matthew Tucker, who was brought back as part of the practice squad, and Henry Josey, now on the Jaguars' practice squad.
"You know now nothing's guaranteed, especially with them two really playing their hearts out, playing some great football," said Polk, who garnered only 11 carries last season, but scored on three of them. "I knew what was at stake. But you've just got to control what you can control, just take it for what it is and what happens happens."
He added: "It's a big relief, but the pressure's on me because I haven't done nothing in a month. So now it's time. Especially now that the season's starting, it's time to go."
Polk, like everyone else, has high expectations for the Eagles' bolstered running back corps.
"The sky's the limit," he said.
Carroll on kick returns
Sproles will also play a role on special teams as Philadelphia's punt returner, but expect the Jaguars' first kickoff to be returned by a different first-year Eagle.
If rookie Josh Huff (shoulder) is not ready to play Sunday (he did not practice yesterday), cornerback Nolan Carroll II will get the first shot at returning kickoffs. Kelly said the way Carroll hits the holes fits well with the Eagles' blocking scheme, but didn't rule out Sproles, Brandon Boykin or Brad Smith also seeing time at the position.
During his rookie season with the Dolphins in 2010, Carroll returned 27 kickoffs for 655 yards. As his role on Miami's defense increased, his job returning kickoffs diminished. He also returned kickoffs a bit during his collegiate days at Maryland, but did not return any in the third preseason game against the Steelers, the only one for which he was active.
"We've done a good job simulating it in practice, guys coming full speed and just tagging off," he said. "We've got a good simulation with that, so when the games come all it is is just [defenders] tackling. That's really it, just more the physical part of it. We've done the game speed so much that things are starting to slow down and it's all timing with us. I've just got to catch the ball and hit it full speed downhill and that's it."
On Twitter: @jakemkaplan