COLUMBUS, OHIO - MARCH 22: Grant Williams #2 of the Tennessee Volunteers reacts during the first half against the Colgate Raiders in the first round of the 2019 NCAA Men's Basketball Tournament at Nationwide Arena on March 22, 2019 in Columbus, Ohio. (Photo by Elsa/Getty Images)

The biggest sleeper of the 2019 NBA Draft is also the prospect most capable of taking the mantle from Draymond Green and P.J. Tucker as the league’s next great small-ball center.

When Grant Williams arrived at the University of Tennessee, coach Rick Barnes took to calling him and teammate Admiral Schofield — the two young men who would push the Volunteers to new heights and cement themselves as legitimate NBA prospects — “fat boys.”

The physical transformation from big kid who could surprise folks to bona fide first-round prospect defined Williams’ time at school and prepared him to potentially become the NBA’s next great small-ball center.

Archetypes define the NBA draft. Executives hunt for the player who can either give their team a bit of what the league’s greats are doing, or limit what those superstars can do somehow. When the Warriors’ dynasty began in 2014, many set out to discover the next Draymond Green — a big man with the versatility to guard all over the court who also had the strength and hustle to be a legitimate center.

Reality quickly set in that the next Green was nowhere in sight.

The Warriors’ greatest challenger not named LeBron James or Kawhi Leonard has been the James Harden-led Houston Rockets, who pushed Golden State to at least six games each of the past two seasons. The Rockets’ success in part has been led by P.J. Tucker and his ability to provide a semblance of Green’s value. Tucker, a veteran who broke into the league in his mid-20s, found a niche following in Green’s footsteps as a small-ball big.

“It’s amazing to be able to have guys like P.J. and Draymond who have done it and opened up the transition for guys like myself,” Williams said at the NBA Draft Combine in Chicago in May.

“I feel like it’s not really about who can score the basketball, because there’s a lot of guys who can shoot it, a lot of guys who can score it, but it’s a matter of if you can truly defend the other end, and that’s what I’m trying to show.”

We may never see another player who can distribute the ball (and lead his team in assists) while also anchoring the best defense in the NBA. Tucker, for example, brings a fraction of Green’s playmaking on offense. So when we talk about the next Green, the conversation mostly centers around defensive versatility.

To get to his level, a player must be able to defend multiple positions, cover for his teammates with a feel for the game bordering on genius level, rebound, and protect the rim. Since entering the rotation full-time in his second season, Green’s steal and block rates have hovered around 3 percent, and he’s grabbed around eight rebounds per 36 minutes. These playoffs reminded us what Green can do when he’s in shape and engaged — snuff out multiple offensive actions over the course of a few seconds and leave teams flummoxed.

The work Williams put in on his body over three seasons in Knoxville led to him cutting his body fat down to 5.4 percent by measurement time at the combine. He cut out processed carbohydrates such as pasta and other starchy foods to get more lean. “Being able to be strong while also being mobile” was a big focus under Barnes, says Williams.

At 6-foot-8 with a 6-foot-10 wingspan, the measurements database NBAthlete lists Green and Chuck Hayes as two of Williams’ top comps. Barnes took advantage of that flexibility this past season, as Tennessee finished the season ranked sixth in the nation, led by Williams and Schofield closing games as the team’s two bigs. There may be no big man in the nation who got a better opportunity to prepare for his new NBA role than Williams’ frontcourt minutes this past season.

Williams flashed incredible defensive instincts patrolling inside.

Against college athletes, Barnes could trust Williams’ IQ to do most of the work to anchor Tennessee’s defense. He may not have the length or strength of Green, but with a frame more like Tucker’s than Green’s, Williams was still able to protect the rim with smart positioning and precise vertical leaping to contain drives.

Also like Tucker, bigger guys who couldn’t speed past Williams were helpless against the Tennessee forward. Williams’ understanding of where to be and how to fight athleticism with angles and positioning won out in most matchups.

When Williams got out on the perimeter, though, his somewhat slow feet and trouble getting low into a defensive stance and push his center of gravity downward made it tough for him to contain small guards.

“It’s going to be about using (my) length, understanding that it’s a quicker pace in the league,” he says. “If you can guard six or seven seconds (on the perimeter), you’ll be good.”

Barnes gave Williams and Schofield the green light to switch onto smaller playmakers late in the shot clock, where he trusted their length to survive long enough to end a possession. The track record is spotty, though the repetitions will surely help Williams’ confidence in similar situations at the next level.

The success of bigger guys defending smaller playmakers driving to the basket is determined in large part by their hips. It’s just improbable to deter a driving wing scorer if you can’t rotate and cut him off before he gets a head of steam.

This will be Williams’ struggle.

“If you force them into a shot that you want them to take instead of a shot they want, you’re good,” he says. “That’s a midrange pull-up or a deep 3 with a contest, rather than letting them blow by and create opportunities for others or get to the rim.”

Harden makes it easy on Green here with the step-back, but you can see right away the difference between sizing up the long, twitchy, fierce Green versus a weaker defender.

Because he is an incredible basketball thinker, Williams knows what he will need to do defensively. The template is in front of him. He improved as a rebounder and turnover creator each college season and has the instincts to earn the trust of NBA coaches.

Williams’ offensive role will be even simpler. Understanding that he won’t reach Green’s level as a playmaker on the move and that he likely will never play with the floor spaced to the degree the Warriors open things up, Williams needs to simply move the ball and make open shots.

That minimal level of responsibility will allow Williams to thrive. Barnes ran the offense through him at Tennessee, which helped develop his court vision and passing skill.

Couple that with a level of hustle that creates second chances and unexpected openings, and Williams is set up to add value on offense even if he’s just an average shooter. This season, Williams shot 33 percent from deep but 82 percent from the line. He also assisted on nearly one fifth of his team’s buckets when he was on the floor.

“It’s never been about putting pressure on shooting the ball, because there are days when you’re going to shoot the ball great and there’s other days when you’re going to shoot the ball terribly, but it just is how hard you compete and what you do to separate yourself,” says Williams after a pre-draft workout in Phoenix.

College teams with top-tier prospects have to juggle maximizing their players’ ability to develop with winning games. Coaches are judged by the performance of the team, not how highly their players get taken in the NBA Draft. Barnes probably veered too far in the direction of giving his once-“fat boys” free reign this season. Though Tennessee lost in the Sweet 16 as a No. 2, Williams got the chance to show NBA teams a skill set tailor-made to fill one of the most coveted and rare archetypes in the game.

The unique combination of physical characteristics, buy-in and high-level skill required to impact the game in the way Green and Tucker do is illustrated by the very fact that only those two guys to mind as elite versions of this type of player.

There are fungible players like Serge Ibaka or Paul Millsap who give you maybe 60 percent of what you need from a true passable small-ball 5. What makes Green and Tucker special is their teams really aren’t sacrificing much when they’re out there at center. That’s the distinction — and the incredibly high bar Williams must reach to be the next guy in this lineage.

Many have been thrust — uncomfortable and unready — into that role since Green’s ascension popularized players like him. Williams spent three college seasons building toward it. If any prospect over the past few seasons can develop into the next small-ball 5, it’s him.