Shortly after Christian McCaffrey arrived at Stanford, Coach David Shaw learned one of his essential traits. “Christian,” Shaw said, “is a man of little doubt.”

McCaffrey carried a broad vision for himself as a football player, a freshman who refused to be classified on others’ terms. In high school, when his coach wanted him to hone a specific skill, he would express skepticism about McCaffrey’s talent for it and watch McCaffrey work like a madman to prove him wrong.

McCaffrey had played multiple positions in high school, and recruiters from other schools doubted he possessed the size and strength to run between the tackles. Before Shaw could broach his usage, McCaffrey looked Shaw straight in the eye, dead serious, and brought it up himself.

“I’m a running back,” McCaffrey told him. “I came to Stanford. I want to run the power play.”

McCaffrey has since shown the football world what he knew then: There is nothing football demands of an offensive skill player that he cannot master. In the process, McCaffrey may have changed the sport.

In his first three years as an NFL running back, McCaffrey has expanded and redefined the position, providing a template for how running backs — maligned as interchangeable, fragile and not valuable — can be the engine of a thriving offense.

On production alone, McCaffrey’s 2019 season makes him an outlier. He leads the NFL with 1,244 yards from scrimmage and 13 total touchdowns, even though the Panthers have already taken their bye. He has gained nearly 20 more total yards per game than any other player. The Panthers have thrown him 52 passes, and he has caught 42 for 363 yards. He has kept Carolina afloat without Cam Newton, positing them at 5-3 heading into a Sunday meeting at the Green Bay Packers.

But the way McCaffrey plays makes him a model. He hardly ever comes off the field, serving as a receiver, runner or decoy. Panthers offensive coordinator Norv Turner can wield him as a pass catcher out of the backfield or from the slot, where he runs polished routes like the son of an NFL wide receiver. He’s a nightmare for defenses, able to punish heavy personnel with his receiving or nickel alignments with his running.

“I don’t mind saying this. It’s not a negative thing at all,” Shaw said. “Because of his race, he doesn’t get put in the category he should be in, as far as people outside the game. People inside the game, they’ll tell you we’ve seen this before. This is LaDainian Tomlinson. This is [LeSean] McCoy. This is in that mold of Marshall Faulk.”

McCaffrey stands among a small handful of other running backs, such as New Orleans’s Alvin Kamara and Arizona’s David Johnson, who are reshaping the position with their versatility, combining the power and speed of a running back with a wide receiver’s skill set.

“The league is shifting,” McCaffrey said in an interview with ESPN this summer. “It’s becoming a smaller league, way more speed-dominant. So you’re seeing more backs like me who can run between the tackles, pass-protect, catch and become matchup nightmares. You also have more receivers who are getting jet sweeps, doing different things with the ball in their hands. A lot of it stems from college offenses. There’s very few pro-style college offenses nowadays, so you see NFL coaches adapting to the players that are coming in.”

That he has buoyed an offense that replaced Newton with Kyle Allen is telling — a running back of McCaffrey’s caliber and diverse skills can carry an offense even without a franchise quarterback. But is he a prototype? Or just an ideal? Can he be duplicated, or only emulated? The answer lies in examining how McCaffrey became the NFL’s next great running back.

For an athlete, McCaffrey hit a genetic lottery. His father, Ed, won three Super Bowls during a 13-year career as an NFL wide receiver. His mother, Lisa, starred on the Stanford soccer team, and her father, Dave Sime, won a silver medal in the 100 meters at the 1960 Olympics. McCaffrey’s uncle played basketball at Duke, and his three brothers all played or play Division I football in major conferences. When Shaw was recruiting McCaffrey, who is still shorter than 6 feet, he saw him dunk over teammates at the end of a basketball practice.

By the time he reached Valor Christian High in suburban Denver, McCaffrey was both too small for a full-time varsity spot but too talented to play on the freshman team. Coach Brent Vieselmeyer gave him opportunities that would let him carry the ball in space but not expose him to dangerous hits. He ran fly sweeps and caught option pitches and screen passes. He worked tirelessly with his father to polish his route running.

From the start, McCaffrey sought to be well-rounded. When McCaffrey was a freshman at Valor Christian, Vieselmeyer would not let him return punts but played him on the line as a rusher — and McCaffrey blocked six punts. He became Valor Christian’s punter, “and he was incredible,” Vieselmeyer said. Early on at Stanford, Shaw tried McCaffrey as a gunner on the punt coverage unit, and McCaffrey is still the best gunner Shaw has ever seen. ­McCaffrey has joked with Panthers Coach Ron Rivera about lining up at safety, which he played in high school.

“He wasn’t tunnel-vision,” Vieselmeyer said. “He’s like, ‘Man I’m going to learn how to catch the ball, I’m going to learn how to play defense, I want to be a great special teamer.’ He was so mature in that regard. You normally have to talk kids into playing special teams. He’s like, ‘Hey, man, I want to compete, I want to ball.’ ”

His competitive drive — sharpened by growing up with three athletically gifted brothers — and work ethic separated McCaffrey. Vieselmeyer recalled enforcing rest as his biggest challenge in coaching McCaffrey, who would interrupt family vacations by doing 500 push-ups on the beach. Once, Vieselmeyer visited McCaffrey at Stanford and took him out for dinner. When he offered dessert, McCaffrey declined and offhandedly mentioned he had not eaten sugar in two years.

By the end of his sophomore season, McCaffrey had bulked up enough to take on inside running. As a junior, he ran up the middle constantly. Recruiters still questioned whether he could do it, which made Vieselmeyer laugh. Shaw said McCaffrey’s film as a junior was the best he had ever seen, jammed with images of McCaffrey hurdling defenders and spinning out of tackles while both bursting up the middle and lining up as a wideout.

At Stanford, McCaffrey declared he didn’t want to be used only on sweeps and reverses, as a gimmick. Shaw was happy to accommodate him. Right away, McCaffrey’s vision and balance were obvious.

“Tight spaces don’t bother him,” Shaw said. “A lot of guys that aren’t the biggest, they don’t want to get in the mess. He loves it in the mess, because he can find creases that other guys can’t find, and when he gets out of that crease, the guys on that second level better be ready. Because he sees them before they see him.”

McCaffrey still embraced a versatile role and Shaw, a former NFL assistant coach for nine years, found different ways to use him. Shaw believed he needed to challenge McCaffrey, and in every game plan he would add two or three wrinkles to give him something to work on during the week. Sometimes, McCaffrey would join wide receivers for one-on-one drills at practice. Shaw still laments a play when McCaffrey ran a perfect stutter-and-go route, and the quarterback missed him. Had McCaffrey decided he wanted to play only slot receiver in the NFL, Shaw said, he would have been a Pro Bowler.

“I have no doubt,” Shaw said. “This guy is as natural a pass catcher as I’ve ever been around, and I’ve been with two Hall of Fame receivers. This guy catches the ball with ease. He’s got feel for body control. His quickness and change of direction are as good as anybody I’ve been around on this level or the NFL level. He walked in the door with that.”

McCaffrey’s intangible attributes also set him apart. On Shaw’s favorite McCaffrey play, he didn’t even touch the ball. Stanford faked a handoff to McCaffrey and gave the ball to fellow running back Bryce Love on a reverse. Most backs, Shaw said, take fakes as a chance for rest. McCaffrey sprinted downfield and made a crucial block as Love ran more than 40 yards for a touchdown.

Though the Panthers picked McCaffrey eighth overall, some teams worried about his durability or even cast him more as a slot receiver than running back. Even after adding so much muscle this offseason that pictures of his biceps became viral sensations, McCaffrey plays at 5-11 and 207 pounds. But two years ago, Shaw told Rivera not to worry about McCaffrey’s durability, that it was another one of his talents.

“We want to make sure we don’t overload him,” Shaw said. “But when you really watch him, he doesn’t take a lot of direct shots. … You don’t usually see him take those big shots, because he is so quick, he is so elusive. He takes a lot of glancing blows. That bodes well for him and his longevity.”

Through three seasons, McCaffrey has not missed a game. He has shown few signs of wear this season while getting 25.8 touches per game.

And so McCaffrey is a Pro Bowl-caliber receiver who leads the NFL in rushing yards per game, who can be counted on to work tirelessly in the offseason and not get hurt during it, a selfless teammate willing to perform any role and able to do them at an elite level. Vieselmeyer, who spent four seasons as an NFL assistant, called McCaffrey a unicorn because the kind of person he is drives the player he is. The NFL may be looking for the next Christian McCaffrey, but it will be a long search without certain success.

“I wish I could have 50 of him,” Vieselmeyer said. “They don’t make ’em like this all the time.”

Read more on the NFL: