PHILADELPHIA -- The tree trimmer is in luck. He is working on this block of South Broad Street just as the Philadelphia Eagles are beginning one of Chip Kelly's hyperspeed practices. His spot in the cherry picker gives him a perfect vantage point on this sunny, early autumn afternoon.

The blaring speakers across the way drown out the tree trimmer's saw while the Eagles begin their session with what looks like a dance class. Players line up across one of the three practice fields. They march forward, knees high, for 20 yards. Then, they return, walking backward this time, without turning.

It's important for the Eagles to get loose before practice because they'll be going full tilt once the first practice period starts. Jim Davis/The Boston Globe/Getty Images

There are two flat screens, roughly the size and shape of play clocks on game day, one on each side of the NovaCare Complex's fields. They have two pieces of information. In small, orange numerals at the top, the screen shows which period it is. In large, red numerals, a clock counts down the amount of time remaining in the current period.

Period 1

On one field, three groups gather at intervals of 20 yards. Each group is comprised of a quarterback, a center, a running back and some receivers. Each unit lines up in unison. Three balls are snapped, three quarterbacks drop back. Almost simultaneously, three balls are thrown to receivers, all open because, well, no one is covering them.

On the next field over, practice squad quarterback G.J. Kinne throws passes down the middle of the field. Cornerbacks and safeties take turns running under them, turning and leaping to catch them.

Nearby, the big guys are starting to line up across from one another. Offensive linemen square off with each other, some using large, foam pads to brace themselves, while others fire out as if the ball has just been snapped. Defensive linemen run similar drills with each other.

Period 4

In the early going, this is pretty much how it looks. Position groups are working together, focusing on specific skills. Only the quarterbacks get small complements of teammates, and their focus is on timing.

At one end of a field, the running backs gather. They are paired off, with each member of a pair stepping into the open end of what looks like a long rubber band. As one player stands his ground, the other clutches a football, lowers his shoulder and runs forward until the rubber band has reached its limits and starts pulling him back. The backs take turns, serving as anchor and then fighting the resistance.

Meanwhile, around the field, a large, rubber ball is being rolled at the outside linebackers. Each one reaches down, pushes the ball away and then sprints toward a blocking sled. After pounding the sled, the player rolls off and heads back to repeat the exercise.

The frenetic chaos of practice, and the preparation for similar chaos on Sundays, is what Eagles coach Chip Kelly lives for. AP Photo/Matt Rourke

Offensive and defensive linemen are grappling with each other. Wide receivers run routes while defensive backs shadow them. All the components of a football play are there, but none of them have been put together yet.

Meanwhile, the tree trimmer's ears are assaulted by what sounds like the iPod of a 15-year-old girl. There are pop hits, dance-club favorites and the occasional old-school rock song mixed in. It is all played very loudly to simulate the noise of a crowded stadium on game day.

"It's controlled chaos," linebacker Emmanuel Acho said. "We have the music blaring. Sometimes, you can hardly hear your teammates. But that means everything on Sunday is a lot slower. When you come out here and you can hardly hear the call, then on Sunday, when you're playing at home and it's quiet when you're out there, then it's very simple. I think we do a good job of stressing ourselves in practice so the game is easier."

That is precisely Kelly's intention, and it is precisely what set cornerback Cary Williams off after a Week 3 win over the Washington Redskins. Williams said it was difficult to play a game on Sunday after playing "three games" in practice sessions in the preceding week. The veteran, who previously played for John Harbaugh and the Baltimore Ravens, said he thought the toll levied by the practice pace was being paid by a lack of energy in the beginning of games.

Kelly met with Williams, who stood by his comments. But it's also true that many players credited the practice schedule with helping them stay fresher last season than they had in previous seasons.

Period 12

Now the practices begin to resemble real football. There is not live hitting, although the Eagles do practice in pads once a week. But the offense and defense line up against each other and run plays.

One of Kelly's principles is that everything is done at the hurry-up pace he wants to operate his offense at in games.

"It's fast-paced," safety Malcolm Jenkins said. "We're getting a bunch of reps in a short amount of time. And then we're getting a lot of different periods. We'll go full speed, then a walk-through period. It simulates how we play the game. We run a 10-play drive, full speed the entire time, and then we sit on the sideline while the offense is up. And we keep doing that rotation the whole practice, so you're getting gamelike repetitions during the week."

Darren Sproles (43) & Co. get a water break and some teaching time before going back at it. Stew Milne/USA TODAY Sports

There is a consequence of that. To have the first-team offense run a drive against the first-team defense -- and then have both squads take to the sideline -- you have to give the second teams a lot of practice time. In the past, the Eagles' backup quarterbacks would get exactly zero practice reps while the starter was preparing for a game. Under Kelly, all the backup players get nearly equal practice time.

When a starter gets injured, that pays off. It's not a guy who is cold and unfamiliar with his teammates stepping into the vacancy; it is a guy who has practiced with and against them all week.

"We get tons of reps here, which is great," said backup center David Molk, who was pressed into action because of injuries in two of three games so far and will start Sunday in San Francisco. "I'm extremely comfortable with how [the other linemen] move and react and shift. It's easy for me."

Period 16: 'Teach'

The sudden silence is jarring. With the music silenced, a voice is audible over the speakers.

"Teach," it says. And for the period that follows, players gather in position groups, around their position coaches, and instructions are given. It's also time for a water break.

But the "Teach" periods underscore that very little communication goes on in the regular practice periods. This is very different from the typical NFL practice.

Reporters who have covered the Eagles for a long time all do a version of Rich Kotite's distinctive nasal honk cutting through a practice session: "Back in the huddle," Kotite would yell, and the players would abandon their misguided formation and trudge back into a circle to be corrected by the coach. Then, they would spread out again, line up correctly and run the play.

Kelly has no use for this. His team doesn't huddle, for one thing. For another, there has never been an occasion in a game in which the coach was allowed onto the middle of the field to make sure the players were lined up correctly. If it doesn’t happen in a game, it doesn't happen in a Kelly practice session. What's the point?

But the "Teach" periods allow everyone to catch his breath and focus on the coaches' instructions. There aren't many of them.

Period 22

There's no rest for the weary, as the all-important red zone drills are about to start. AP Photo/Elise Amendola

By this point in a practice, everyone has been on the field for almost two hours and is getting tired. But this is the point at which Kelly conducts his red zone drills, the most intensely competitive aspect of any NFL practice.

The importance of these drills was brought into sharp relief by the Eagles' come-from-behind, Monday night victory over the Indianapolis Colts. During that comeback for the Eagles, Period 22 became a rallying cry.

"No one rises to the occasion," Kelly said after the game. "You always sink to your level of training. That's how we trained them. You heard our guys talk about it after the game. This is no different than Period 22 on a Wednesday or Thursday for us."

You heard versions of that in the locker room afterward.

"Some people were saying, 'This is just like Period 22 for us,'" Jenkins said that night. "We practice at such a pace that, when we get into the fourth quarter, guys are fresh. Guys are still at full speed. This is what we train for. It’s Period 22."

Period 26

The players are on the grass, forming a large circle. They are on their backs, legs up, stretching one last time. Each player has a long rubber band that allows him to stretch his tired leg muscles. They are already beginning the recovery period that will allow them to be strong the next day.

Cary Williams wasn't kidding when he spoke about the intensity of an Eagles practice: They aren't a joke. AP Photo/Matt Rourke

Aides scurry around, collecting the tiny GPS devices players wear. These monitor movement and help the training staff keep track of how much each player is exerting. This information is used to help create the famous post-practice smoothies players consume and to tell coaches which players need a little time off.

"Not many teams have done that, as far as catering to the individual athlete," said Acho, who spent time with the Giants last year. "Whether it’s their own meal plan or their own workout regimen, their own recovery regimen, everybody has something individualized for them. It's very unique to this organization."

Bill Davis knows. Unlike Kelly, who arrived in the NFL last year after many years coaching at the college level, Davis is an NFL lifer. His father, also named Bill, was an assistant coach and executive with the Eagles and other NFL teams. Davis himself has been an NFL assistant for more than 20 years. This is his third time as a defensive coordinator. He has fully embraced Kelly's new world order.

"We train in a great way," Davis said. "The sports science we have, the way we handle it, there's no concern. I actually think we are the strongest team in the fourth quarter, and it shows. We keep finishing the games. Where others don't have it in the tank, we have it in the tank, and it shows. This is an elite program. I've been with 10 different organizations, and it's not even close."