Jim Schwartz needed to watch all 11 players when the defense was on the field during Sunday's practice. But the Eagles' defensive coordinator knew most observers focused on only one player: cornerback Ronald Darby.

Darby, who was acquired Friday from Buffalo in a package for Jordan Matthews and a third-round pick, practiced for the first time. Schwartz didn't waste a minute inserting Darby into the starting lineup. There was no slow transition for Darby; the Eagles treated him like the No. 1 cornerback, playing him on the left side during full-team drills. Jalen Mills and Patrick Robinson also rotated in with the first-team defense, but Mills played only on the left side.

"It's tough when you come in and you've got one day to try to get up to speed, and there were a couple signs of that where we had a miscommunication," Schwartz said. "It really wasn't a miscommunication, it's just he's not up to speed on a lot of the calls. But we tried to limit it, mainly a lot of man-to-man just so it would stay that way."

Still, it was a first glimpse of the player designated with upgrading the team's heretofore cornerback problems. Schwartz watched film of Darby before the trade. His analysis matched most scouting reports: talented young player, can play on the outside, "had a really good rookie year" before an "up-and-down" second season.

Darby's quickness was as advertised; wide receivers didn't burn past him because of Darby's recovery speed. He was beaten on a deep pass to Alshon Jeffery during a seven-on-seven period, but that was more the 6-3 Jeffery using his size to go over top of the 5-11 Darby.

"Big receiver, he'll help me a lot with physical receivers," Darby said.

It was not a coincidence that Darby played on the left side. That was where he played during his first two NFL seasons, with Stephon Gilmore playing on the right. Schwartz wanted to put Darby where he was comfortable. As Darby learns the Eagles' defense, Schwartz said they will move him between the right side and left side in practice. The benefit of doing so is that if the Eagles wanted Darby to shadow an opposing team's top receiver during games, he's able to play on both sides. Schwartz indicated that Darby is best as an outside cornerback, so don't look for him to play in the slot.

Schwartz did not rule out using Darby to shadow an opposing receiver. He said he's done it in the past, and it will depend on size and speed matchups. But it's too soon for Schwartz to make that determination.

Learning the right side shouldn't be an issue for Darby when that time comes. He said he was playing on the right side this summer with the Bills in Sean McDermott's scheme. That relied on more zone concepts; Darby was back playing man-to-man defense on Sunday, so he said he was familiarizing himself with how he used to play.

"I'm trying to get a feel for things," Darby said. "We play a lot of man, and that's something I'm used to. I'm allowed to get up there and press."

Schwartz reserved judgment on how Darby did because, as he mentioned, he was focused on all 11 players. He emphasized several times during his news conference how excited the Eagles are to have Darby. He did not speculate why the Bills would trade a 23-year-old with Darby's ability.

"You have to ask somebody else on that," Schwartz said. "We're glad to have him here."

It's likely that Mills will be the other starting cornerback, although Schwartz did not put a timetable in making that determination. If Robinson is on the 53-man roster, his experience in the slot can be beneficial. Schwartz pointed out how Robinson did it in New Orleans, San Diego and Indianapolis, which is why the Eagles tried him there on Saturday. The caveat is that Ron Brooks, who has played there most of the summer, is sidelined with a hamstring injury. The Eagles also tried Aaron Grymes in the slot, and they've used a three-safety package that moves Malcolm Jenkins to the slot with Corey Graham taking Jenkins' spot.

"We'll play all the different combinations and see how it goes," Schwartz said of figuring out the cornerback depth chart. "We've got a lot of ground to cover before then."

The Eagles can use that time to get Darby comfortable in the defense. Part of the reason he had a sophomore slump was the Bills' instability at safety. If the Eagles can keep Jenkins and Rodney McLeod healthy, Darby can benefit from playing with one of the NFL's top safety tandems. McLeod is often the deep safety, so their communication will be critical.

"Making sure we're all on the same page, speaking the same language, is tough with him just being traded," McLeod said. "It's a whole new type of communication. Guys run similar coverages but different wording. So it's just getting our wording down and then our calls. …And from there, he's just going to play ball."

McLeod said it will take "a couple of weeks" to know how to play off each other. On a specific call Schwartz makes, McLeod said he'll need to know where Darby is going to be so there are no missed responsibilities.

That's why it helped that the Eagles didn't waste time easing Darby into the rotation. It was clear he would be the starter from the moment the Eagles made the trade, and he has one month before the season opener to make up for lost time.

"I didn't know what to expect, to be honest," Darby said. "I'm just going day-by-day, continuing to improve."