During a team period earlier this week, Jeremy Maclin found himself lined up one-on-one against cornerback Bradley Fletcher.
Maclin got an outside release and headed straight up the sideline, but at about 15 yards downfield, he slammed on the brakes, turned around, flashed his hands late and caught a Nick Foles pass that was already there waiting for him.
It's the back shoulder fade - a weapon Foles, Chip Kelly and the Eagles are looking to add to their arsenal as they prepare for 2014.
"I think that's just something that's a great addition to the offense," Foles said. "We've always tried going over the top, [but] that's something that you see a lot of the guys like [Drew] Brees, [Aaron] Rodgers, [Peyton] Manning, [Tom] Brady, they do a really good job if a guy's overplaying their receiver, it's just one of those things you have to have a feel with it. You want to give your receiver an opportunity to catch the ball. So it's something that we're working on. You want to be able to connect in any way possible, so it's just a great throw on any level - high school, college or the NFL."
Beating man coverage has become an obsession for the Eagles' coaching staff this offseason. Last year, the most common tactic for slowing them down was to play man coverage with a single high safety. And Kelly is not expecting that to change in 2014.
The back shoulder fade is a pass that can be completed even when cornerbacks have very good coverage. Asked how to defend it, Nolan Carroll II started to shake his head.
"You can't, man," said the Eagles cornerback. "You get lucky with it. It's so hard because your back is turned and the receiver is looking at the ball, so he knows if it's gonna be a back shoulder or not. And normally around the league, it's 10 yards and they kind of turn their back. So for us, we're taught to stay on top, but at the same time, if you throw the back shoulder, we've kind of gotta stop the brakes and break up the pass. And it's so hard when you're going the other way, and the receiver's looking back and he knows what's happening. He can just turn his back and make an easy completion, 10 or 15 yards. So it's hard for us. It's a 50/50 ball, if you can get lucky."
Here's an example of Tony Romo and Terrance Williams completing a back-shoulder throw against Cary Williams and the Eagles last year.
It's 3rd-and-5, and Williams has man coverage on the outside.
He does a good job of sticking with the receiver, but in the above frame, Romo is already releasing the ball. You can see that Terrance Williams' head is turned back to the line of scrimmage.
"It's one of the hardest throws you can defend as a corner," Cary Williams said. "Those guys can see the ball the whole way through and they can make their adjustment when necessary. So you get a good quarterback to throw it at your back, some things you can't do anything about."
Added Malcolm Jenkins: "It's tough because it's the opposite of what you're taught. So if you're in good position as a DB, normally that means that the back shoulder's open. That means you're in face of the receiver and they throw it back and away from you, so it's a tough play."
Here, you can see Terrance Williams has his body turned and is ready for the ball. Cary Williams, meanwhile, has his back to the line of scrimmage.
On deep balls downfield, Eagles cornerbacks are taught to look at the eyes and the hands of the wide receiver when they're face-guarding. But on back-shoulder throws, the technique is different.
"It's really reading his hips, but it's so hard because you're reading him and then next thing you know, he just swipes you by and turns around and it's a completion," Carroll said. "So you've just gotta try to stay in his hip as much as possible and get a good feel for when the back shoulder's coming. And when you're in press, just go through your progressions as far as the 5, 10 yard area. When you feel it, that's when you can kind of break on it."
Others, like Nick Saban, teach to read the upfield shoulder.
"It's really all about the finish - being able to kind of get your hips around and disrupt the receiver so that he's not making an uncontested catch," Jenkins said. "Because it's hard for them too. They've gotta get their body around and still track the ball. But if the quarterback throws it right, it's hard to defend. And once you do start defending it, they'll throw it over the top. So it's one of those things you've got to continuously get reps at it, and if you know a team is doing it, then you play for it a little more."
Jenkins has plenty of experience from his playing days in New Orleans going up against one of the best back-shoulder throwers in the NFL, Drew Brees.
"Brees was good enough where he changed it up a lot," Jenkins explained. "He really reads your position, so if you're on top, he's throwing back shoulder. If you're low, he's gonna throw over top. And that puts you in a position where you can't defend it."
"That's what they're coached to do - throw it at the back of our head..." Cary Williams said. "We don't know where they're going. They know where they're going so they can see the ball, so it's tough."
Added Kelly: "Coverage is tight and you have to beat the guy over the top and maybe the way to beat the guy is to throw it behind him."
From an offensive perspective, the keys are timing and chemistry. The quarterback and the receiver have to be on the same page, or these throws will be ugly. The receiver has to turn around and flash his hands as late as possible to limit the time the corner has to catch up.
"It's just another weapon to have," said Maclin. "I think it's something that we'll have. It's not necessarily what we're looking for. It's just something that we'll have in our bag of tricks that we can pull out. It's probably the single hardest throw to defend in football, so it'll be good to practice that so we have it down."
The key for the receiver?
"Running the fade, running the go-route first," Maclin said. "Then adjusting to the ball. When you start looking for the back shoulder, that's when it can go sour."
Bigger receivers obviously have an advantage because if the ball is thrown high and to the outside, they can go up and get it. But Cary Williams said that factor can be overrated.
"I think the best two guys throwing it are Peyton Manning and Tom Brady throwing those things," he said. "Those guys do a lot of work. They do it in the game. Regardless of what size the receivers may be, they always seem to fit it in there at the right time, the right place. I don't know if it's a trend. But I know those guys, in order to be great, you've gotta be able to throw the back-shoulder fade."
As Foles looks to take the next step in his development, he clearly agrees with Williams' assessment.
"I definitely always want to improve my game, so what's the best way to improve your game?" he said. "Watching the ones who were before me that were the great ones and learning why they were so great at what they do. And watching the film, all the great ones were able to throw back shoulders. I think the big thing is throw the ball where only their receiver had an opportunity to catch it and the DB can't make a play."
Added Pat Shurmur: "I think they can be very effective if they're thrown with the right timing and at the right spot. So it's just one of the things guys work on. We try to take advantage of every opportunity to get the ball down the field, and that is just another way to do it."