Some NFL players change their game as the sport evolves. Then there is Darren Sproles. The 5-foot-6 running back, who just started his 15th year in the league, has let the game change around him. At 36 years old, Sproles leads all active NFL players in all-purpose career yardage. The NFL celebrates its 100th anniversary this year, and when they celebrate their 200th, Sproles will still be breaking tackles to convert fourth-and-2s.

“The difference between when I came in and now is that you could only get your touches sometimes because there was always going to be one back who was the focus. Now every team has three,” Sproles, a legendarily good third running back, said. “The other difference is that when I came into the league, they wanted big, tall backs. I feel like when the years went on, they wanted [the role that I play].” He mentions how running backs catch more passes now. In short, the current NFL resembles football as Sproles has always played it. He never changed; everything around him did.

It is important to study Sproles now, not just because of his production, but because the role he has carved out for himself is the story of modern football. In the 14 years since Sproles entered the league, space has become the lifeblood of the sport, and Sproles knows how to find it and use it. He is a football success story—one that continues this year after the Philadelphia Eagles re-signed him this month—a lesson in defying the aging cycle of a running back, a position where careers are supposed to be shorter than ever. He’s created value for the teams he’s played for throughout his career. Sproles’s 2008 season still stands as the most receiving yards a running back has gained per route run since Pro Football Focus started tracking it—even including this new generation of elite pass-catching running backs; he has made $43 million in an era where running back pay is declining; he is smaller than the vast majority of players at his position in an era in which size matters less and less. He has had some good luck by playing for coaches who know how to use him—Norv Turner with the Chargers, Sean Payton with the Saints, Chip Kelly and Doug Pederson with the Eagles—and there is a lesson in that, too.

On a scorching July day, Sproles stood on an NFL field for another training camp. His career longevity has exceeded his own expectations. “My goal, always, was 10 years and everything after that was a bonus,” he told me. But the biggest reason he was still on this field is that he is uniquely Darren Sproles. He is not the first short running back—they’ve always existed, but they’ve rarely done as much as well as Sproles. He did not create this era of football—a smaller, faster, more flexible game—he simply outlasted the old one and stuck around long enough to play in a new one perfectly suited to him. He has been banged up for a lot of it (he has suffered major injuries in each of the past two seasons) but has shown enough—including starting one of Philadelphia’s playoff games in January—to convince the Eagles to bring him back for his sixth season with the team.

I wanted to talk to Sproles—and those around him—because in many ways, he is one of the avatars for what football has become and where it is going. His ability to get the yardage his team needs has been a hallmark of his career—even if he’s injured, even if he’s not the same player he was a decade ago. This is not an accident. “I learned you are only going to get the ball a couple of times,” he said. “So whenever I get it, I have to make something happen.”

Nothing, in fact, about Sproles is an accident. When Sproles was growing up in Olathe, Kansas, the offense his Pop Warner football team ran was simple: Pitch to Sproles on the left or right side and watch as he runs for a touchdown. Before Sproles turned 10, his father, Larry Sproles, got a memo from league officials. “They changed the rules,” Larry Sproles said. “They sent me a memo that said the game wasn’t very fun for other kids. He was mercy ruling them so much.” The new rule stipulated that Sproles had to run in between the tackles every time he touched the ball. If you’re looking for a superhero origin story, this is it. Sproles had to learn how to create space in the middle of the field instead of on the edges. He learned how to make cuts close to players and how to exploit small holes. He could already run fast—now he had to learn how to run fast in a crowd.

Sproles’s game makes sense the more you learn about his childhood. Larry Sproles, who was an undersized running back in college, knew Darren would need to catch passes, so he made his son catch 20 of them in a row without dropping one and, more importantly, without using his body to trap the ball. “I also told him ‘We’re not going to get any taller, but we can get stronger,’” Larry Sproles said. “So he got into the gym, and that man still goes to the gym. Pound for pound, he’s still one of the strongest guys in the league.”

“They changed the rules. They sent me a memo that said the game wasn’t very fun for other kids. He was mercy ruling them so much.” —Larry Sproles

Inside the Eagles locker room, I asked a few of Sproles’s teammates for their favorite moment from his career. It is generally understood that there are two distinct types of plays that define Sproles. The first is a play where it seems as if Sproles has no chance to get out of a situation but then does: The defense surrounds him, he uses his blockers, his legs keep moving, his shoulders go down, and all of a sudden he’s got a first down or a touchdown. The other is the exact opposite: A defense, inexplicably, forgets all about him and he’s wide open in space running down the sideline. These plays tend to repeat themselves over and over again. One of the best examples of the former came last December against Washington. The MVP of this play was Eagles offensive lineman Jason Kelce, but Sproles was the very best version of Sproles he can be:

“Kelce was doing Kelce things, and Sproles had to get about 8 yards to score, but it wasn’t a normal 8 yards,” said fellow Eagles running back Corey Clement. “That was the fastest 8 yards I’ve ever seen. He can keep doing this. He’s got three more years left in him if he wants.”

Clement said Sproles uses his center of gravity better than almost anyone. “I’ve never seen a guy get so low and get out of cuts as fast as he does. I keep picking his brain, but sometimes he doesn’t know how he does it. If you look at the film, he knows what he’s doing before he knows what he’s doing. It’s kind of weird.” Outside the Eagles locker room, I show Sproles the play in question. “You view Kelce as a fullback,” he said. “You find the first little seam then just keep your legs moving. Never stop your legs from moving. You see this little hole and say, ‘You know what? Let’s just try to get in there.’”

Pederson, Sproles’s current coach, said these types of plays come as a result of Sproles’s vision, work ethic, and size. “He can see things, make quick decisions, and then his stature is small, and he can hide behind offensive linemen and kind of slip through the cracks,” Pederson tells me.

“If you look at the film, he knows what he’s doing before he knows what he’s doing. It’s kind of weird.” —Corey Clement

I asked Eagles pass rusher Brandon Graham, who has defended against Sproles when they were on opposing teams, what it is like to chase him. “Don’t be tired trying to go against him. This boy never gets tired. You have to be in shape going against Darren Sproles because he’s going to give you the same tempo on every play. In space he is one of the best,” Graham said. “He’s real low to the ground, and he’s thicker than you think.”

Sproles being more than you think—whether it be strength, or speed, or something else—comes up a lot when talking to his teammates and coaches. One Eagles lineman, Lane Johnson, told me that because Sproles is smaller than most backs, no one notices that he’s a good pass blocker. Because teams are still underrating Sproles, he tends to disappear to defenses. This was especially true three years ago, in the other kind of Sproles moment that Eagles players love to talk about, when teams lose sight of him:

Sproles’s ability to disappear is legendary. He plays a sport in which defenses plan to account for every blade of grass, and yet he finds yards of space. “[Artie Burns] was reading the quarterback,” Sproles said of his touchdown catch against the Steelers. “He thought the quarterback was about to run, and as soon as I saw him turn around, I just turned up the field deep.” Even though this play occurred on third down, Sproles said defenses actually let him disappear more on first down. His reputation as a third-down killer is so solidified by now that defenses key in on him on third and play more traditional defense in first, letting Sproles slip by.

“It’s easy to lose him, especially with a mobile quarterback like Carson [Wentz], because guys lock in on Carson,” said Boston Scott, another 5-foot-6 running back on the Eagles. “Is he going to scramble? What’s he doing? And with Darren being smaller it’s easy to lose him. The game has been evolving, the athletes are getting more freakish, and it’s been amazing to see him accomplish what he has.”

I asked Sproles whether he felt he was born too early, or if 1983 was just right. He said he thought he was too soon, but that even if he was born in, say, 1990, he would still have entered a league in which teams underrated smaller players. He said he realized in 2011 that the role he’d carved out for himself was spreading to other teams when the Falcons drafted and utilized Jacquizz Rodgers. Rodgers, who was born in 1990, is currently without an NFL team.

“My goal always was 10 years, and everything after that was a bonus.” —Darren Sproles

There’s a sort of trade-off: Sproles was never the focal point of his team’s offense, but this allowed him to stay in the league years longer than if he had been. He’s run the ball 715 times in his career—for comparison, Sproles’s former Chargers teammate LaDainian Tomlinson rushed the ball 711 times in his first two years in the NFL. Though he’s been targeted 737 times on passes and returned punts and kicks in his career, he’s faced a far less grueling workload. “It worked out the way it should have worked,” Larry Sproles said when I asked him what would’ve happened if Darren was given a more traditional workload. “His career wouldn’t have been as long.”

The Eagles are Sproles’s third team. He believes the first two he played for—the Chargers, who drafted him in the fourth round in 2005, and the Saints—gave up on him too early, which he attributes partly to not being a traditional running back. Teams worried that defenses were keying in on him too much and that his production would suffer. He thinks the Saints pulled the plug earlier than the Chargers. The Saints, he said, “gave up on me.”

“Why?” I asked him.

“Who knows?” he replied.

I asked him whether he has a chip on his shoulder from the way things ended in New Orleans. “Always. Always,” he said.

After the Saints traded Sproles to the Eagles in 2014, Drew Brees called him a “once-in-a-lifetime” player. He was right, but even Brees may not have known Sproles would still be on a roster five years later. The odd thing is that the entire league has shifted toward Sproles’s style, and he’s still once in a lifetime.