This story appears in the Feb. 11, 2019, issue of Sports Illustrated. For more great storytelling and in-depth analysis, subscribe to the magazine—and get up to 94% off the cover price. Click here for more.

The story of college basketball this season can be told from Z to Z. On one end of the spectrum is Duke freshman Zion Williamson, the presumptive No. 1 pick in the NBA draft, a 6'7", 284-pound athletic marvel who needs FAA clearance before he dunks. He is the driving force behind a national championship contender. On the other end is Michigan junior Zavier Simpson, who is (at most) 6 feet tall, and scores 9.1 points per game. He is also the driving force behind a national championship contender.

At least five Wolverines have a better chance at an NBA career than Simpson does. Sophomore 6'5" shooting guard Jordan Poole, who sank a buzzer-beater to oust Houston in the second round of the 2018 NCAA tournament, could play himself into a first-round pick. Freshman Ignas Brazdeikis, the team's leading scorer at 14.5 points per game, has the body (6'7", 215 pounds) and skill set of a 25-year-old. Junior Charles Matthews has NBA athleticism and defensive ability at 6'6", though not an NBA shooting stroke. Jon Teske, a 7'1" center, would have been a first-rounder a generation ago; even in this small-ball era, he may get drafted. Sophomore Isaiah Livers is a tantalizing talent at forward.

Simpson? He gives this self-scouting report: "I'm not quick enough, I'm not fast enough. My finishes are above average. My shooting is average. My ballhandling is average. My court vision is above average. Strength is definitely there. But overall I feel I'm pretty average." Yet since Simpson became the starting point guard in January 2018, the Wolverines are 43–8, including 23–3 this season. His expertise is not creating highlights but preventing them. Studs like Zion spend their brief time on campus showing that they don't belong in college basketball. Zavier had to prove that he does.

A year into Simpson's college career, even his coach was skeptical. John Beilein is known as an offensive whiz and a straight shooter. In the spring of 2017 his freshman point guard was neither.

Xavier Simpson, as his name was spelled then, hadn't developed into Beilein's kind of point guard. His shot was balky, his playmaking suspect, his head too hard. Simpson had backed up senior Derrick Walton for a season, and now here was Beilein, telling him that Michigan would bring in a graduate transfer to compete with him and with incoming freshman Eli Brooks. Even worse: Beilein was not sure who that graduate transfer would be; he just knew he needed somebody. The conversation was cordial, but Simpson says now, "I felt disrespected. I felt like they spit in my face."

Simpson walked out of the meeting and called his parents in Lima, Ohio. He sounded glum. But he also believed what he was too polite to tell Beilein: The program was missing something, and he was the guy to provide it.

Beilein, 64, has a reputation for being as orderly as the silverware he places in the dishwasher—he has been to known to demonstrate the proper technique to his family—and as clean the dishes he pulls out. (When his wife, Kathleen, wanted him to autograph a basketball for his own doctor, Beilein made her go through the university's compliance office.) His emphasis on intelligence, skill and smarts has produced some beautiful basketball teams over his 12 years in Ann Arbor with nary a hint of scandal, but Simpson thought Michigan was not tough enough.

Toughness is not just Simpson's strongest trait; it is the one he cares about most. He was tough before he was a basketball player. When he was a little boy, a cousin called him a monster. His grandfather called him the Tasmanian Devil. His mother, Bobbie Carter, says, "He had no friends." Once, a day-care provider called Bobbie to complain that three-year-old Xavier had stuffed a baby in a garbage can. (Lest the story get twisted: It was more of a gentle placing in the garbage can. The baby was fine! Thanks for your concern.)

Xavier asked his mom why everybody thought he was a bad kid. She would say, "You're not bad. You're curious." Where others saw an agitator in training, she saw a restless ball of energy. In time he channeled his enthusiasm in a more socially acceptable way. He became a leader before most kids know what leaders are. He would ask classmates, "You down with G-O-D?" Then he would come home and boast: "Mom, I got three kids saved in school today!" He says now, "I knew how much clout I had with other kids."

If Simpson's identity was tied to being the best player on the floor, he probably would have transferred as soon as grad student Jaaron Simmons arrived from Ohio to take his spot; he would have lunged for more playing time and a chance to prove himself, as so many players do today. But Simpson thought leaving would be weak. He stayed and became tight with Simmons instead. (Simmons, who is now playing pro ball in Switzerland, says, "It was an easy relationship to build.")

At the start of his sophomore year, Beilein discovered that Xavier's given name was actually (and mistakenly) spelled Zavier on his birth certificate. (His parents meant to change it but never did.) The straitlaced coach suggested it would be proper to switch to spelling his name with a Z. Simpson's good friends still call him X. His number is saved as X in each of his parent's phones. But his dad, Quincey, says, "For what he is trying to do, the small things don't matter."

Simpson earned the starting point guard job in preseason practice ... and then he lost it to Brooks. Bobbie went to Ann Arbor on Nov. 26, watched her son play 13 minutes in an 87–42 drubbing of UC-Riverside and started to vent about Beilein. Her son cut her off: "Mom, don't do that. He's a good coach. He knows what he's doing. Just pray for him." Bobbie thought, "I don't want to pray for him!"

Simpson says now, "I don't feel like that's manlike to go tell my mom. That's immature, extremely soft."

He earned his starting job back by the Jan. 6 game at Illinois, kept it and met Beilein halfway: He became more like the point guard Beilein wanted, and Beilein's program became more like what Simpson envisioned. In 2016–17, Michigan's defense was 69th in the country in Ken Pomeroy's adjusted rankings. Last year it was No. 3 as the Wolverines won 14 straight games heading into the NCAA tournament and then made it all the way to the title game. This year it is No. 2. These are, by far, the two best defenses Beilein has ever had in 27 years of college coaching. "It was pretty," Simpson says, "but now it's gritty with the pretty."

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In order to score, any Michigan opponent must first shed Simpson. Assistant coach Luke Yaklich, who is effectively Beilein's defensive coordinator, says, "You probably have to go through 30 ball screens as a point guard on an average night." Michigan sends Simpson over the top of 95% of them, according to Yaklich. That allows Simpson to prevent a quick shot, then he is strong enough, smart enough and (despite what he says) quick enough to keep his man in front of him. He forces the offense to restart as the shot clock ticks down.

Simpson has an uncanny ability to move laterally, or even through a screen, and still use his hands to disrupt the ballhandler. Ask him where he got it, and he says, "Boxing. Streetfighting."

He is kidding. But Simpson's biggest influence on the team has been instilling a fighting mentality. Sometimes he intentionally bumps into teammates between drills, just to get in their heads. Yaklich is still in awe of one play last year in practice when Simpson got over a screen, deflected the ball, dove for it but didn't get it, hit his head on the floor, bounced up into a defensive stance, then stole the ball again. The Wolverines roared.

Simpson talked about a pit-bull mentality in a meeting last season, and his teammates embraced it. After that, a picture of a pit bull was hung in Michigan's locker room before every game. Coaches hissed at Simpson from the bench, saying, "Get him!"

The Wolverines now understand what his teammates at Lima High knew: If you let your man score, Simpson will let you hear about it. Matthews, a transfer from Kentucky, has become a dominant wing defender. Teske now plays the kind of back-end D everybody used to want: long and strong enough to body big men in the post, but agile enough to average 2.2 blocks. Poole, the team's biggest three-point threat, is a scorer at his core—Beilein has said he has "an overdose of swag"—but he knows he has to defend, too.

Last summer, after Michigan's 79–62 title-game loss to Villanova, Simpson got a Razors Edge pit bull. He named it Sosa because "I don't want my dog to have no name like Billy or John. I wanted a name with a little swagger." Sosa has since relocated to a relative's house after neighbors in Simpson's apartment complex complained. He is coping without Sosa, though he still stews at the injustice.

The Wolverines, meanwhile, don't go anywhere without their lead dog. Ask Michigan staffers what happens when Simpson leaves the floor, and they laugh, because he rarely does. He is averaging 35.9 minutes in Big Ten play. "This year teammates started going a little too far and started barking at me like I'm a dog," he says. "I'm not an animal."

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Beilein gets visibly excited every September as the season approaches, but he never tells his family if he thinks his team will be good. His players are his students. No matter how talented they are, he looks forward to teaching them. When Beilein interviewed prospective assistants two summers ago, he took the unusual step of asking for video of them in practice. He wanted to see how they taught.

Simpson is still not Beilein's ideal point guard, but he has become one of his best students. As Beilein said last spring, after a Final Four win over Loyola-Chicago, "He's stubborn sometimes, but he gets it now, because he can see his growth." On team flights Simpson borrows assistant coach Deandre Haynes's computer so he can watch video, often of practice. His only individual goal this year is to be the Big Ten Defensive Player of the Year. (In fact, he's a strong candidate for national defensive player of the year.) Other than that, he just wants to win games.

Since last season he has improved his jumper. He has added a hook shot, which is not a skill most point guards work on and isn't likely to impress NBA scouts. But that hook has already helped Michigan win games. His most important offseason move, though, may have been working as a counselor at Beilein's camp last summer.

While the rest of his teammates tried to help the elementary and middle school kids have fun and learn the game, Simpson made his do push-ups. He was so fired up that he repeatedly had to be told to go back to the coach's box during games. His team did not win a championship. Simpson blames the refs, all of whom work in the Michigan basketball program. "They were cheating me," he says. "They saw how engaged I was and they thought it was unnecessary."

The accused all laugh at the allegations. But they are not surprised. They know now what they didn't know two years ago: This is Zavier Simpson.

He says, "I can see myself as a Division I coach. I feel like I could be a dominant coach: the respect that Coach K gets, the X's and O's like Coach B, sending players to the league like Coach Cal. That's my goal. I'm sure."

Zavier wants to mentor the Zions of the world. But first he will try to beat them.