Omari Spellman climbed to his feet, turned toward the Warriors’ bench and unleashed a yell.

A few months ago, Spellman wasn’t comfortable doing much on offense beyond catch-and-shoot jumpers. But in that moment Thursday in Minnesota, he had just caught the ball at the top of the arc, pump-faked, dribbled through traffic and thrown down a one-handed dunk over the outstretched arm of forward Jordan Bell.

As Spellman stepped to the foul line for an and-1, he thought — if only for a moment or two — about how far he has come since training camp. After a disastrous rookie season with the Hawks made him question whether he even belonged in the NBA, Spellman, 22, has rediscovered his self-belief while playing with the Warriors.

No longer worried that a slight mistake could land him on the bench, he is free to crash the offensive glass and deliver highlight-worthy dunks like Thursday’s. Some in the Warriors’ organization are beginning to view Spellman, whose third-year option was exercised in October, as a potential franchise building block.

His stats are up in almost every major category from last season. As he illustrated in Saturday’s 23-point, four-steal gem against the Pistons, Spellman — down 55 pounds from when Golden State traded for him last summer — is an instant-energy big man capable of defending multiple positions, hitting open 3-pointers and providing important hustle plays.

“I think Omari has absolutely earned more minutes,” Warriors head coach Steve Kerr said. “Sometimes circumstances turn if you have the fortitude to keep working and remain patient, like he has.”

This is the type of player Atlanta had hoped Spellman would become when it drafted him 30th overall in 2018. What Hawks general manager Travis Schlenk couldn’t predict, however, was how Spellman would handle all that the NBA demands.

A five-star recruit who played big minutes for a national-championship team during his lone season at Villanova, he had experienced little on-court adversity before he joined Atlanta. When he struggled to contain NBA big men and saw his minutes plummet, Spellman became despondent, eating away his frustrations and gaining 40 pounds midseason.

Today, he recognizes that he was depressed and needed help. But in July, when the Hawks dealt him to the Warriors for center Damian Jones and a 2026 second-round pick, Spellman broke down in tears because he felt like a failure. If the team that drafted him had given up on him after one season, what was stopping Golden State from moving on from him just as quickly?

“I had lost so much confidence in myself and my abilities,” Spellman said. “It felt like everything that could go wrong was starting to go wrong. It was a snowball effect.”

Monday’s game Who: Warriors (9-28) at Sacramento (13-23) When: 7 p.m. TV/Radio: NBCSBA/95.7

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Even as he overhauled his diet, rededicated himself to the weight room and began to shed weight, Spellman was wary of his new team. Player-development coach Aaron Miles, who works closely with Spellman, concentrated early on making their relationship about more than basketball.

After breaking down video and going over the upcoming game plan, Miles talked with Spellman about current events, relationships and handling expectations. In practices, when Spellman turned down an open jumper, Miles yelled, “You got to take that!” Gradually, Miles noticed Spellman feel more at ease.

“Player development has so much more to it than the on-the-court aspect of the player,” said Miles, who is in his first season with Golden State after two years leading the team’s G League affiliate in Santa Cruz. “It’s more just the off-the-court stuff, getting to know them and what makes them tick, what’s the driving force behind what they’re going through.

“You can line up some of the things that are happening on the court with some of the things that are going on off the court. Managing that allows a player to be relaxed once he comes on the court.”

When his depression was at its worst in Atlanta, Spellman started to see a therapist, who encouraged him to delete his social-media accounts and stop placing so much value in others’ opinions. During their sessions, Spellman learned that self-belief must come from within — not any outside circumstance.

With this in mind, he has worked to rein in his emotions when mistakes mount or playing time drops. Late last month, when Spellman failed to log double-digit minutes in three straight games, Kerr was pleased to see him not pout.

On Saturday, two days after he dunked on Bell, Spellman bodied up his defender, caught the ball in the key, turned and hammered home a one-handed slam over two Detroit players. Instead of letting out a yell this time, Spellman, straight-faced, jogged back downcourt.

“Not long ago, I would never have been able to do stuff like that,” Spellman said. “I just didn’t have the confidence. But right now, I’m believing in myself and reaping the rewards. It feels good, man.”

Connor Letourneau is a San Francisco Chronicle staff writer. Email: cletourneau@sfchronicle.com Twitter: @Con_Chron