“He has everything you want. He’s athletic, he can run the floor, space the floor vertically, shoot, finish with both hands and protect the rim,” Dinwiddie said. “Right now, the only thing you can knock him for is not being physically imposing, but he’s only 20 years old, and all of that is going to come with time. If that’s all you’re missing in your game, you’re doing really well.”

Allen’s father, Leonard, was a standout center for San Diego State from 1981 to 1985 and held a school blocked-shot record that was broken in 2015. The Dallas Mavericks picked Leonard Allen 50th over all in the 1985 draft, but he didn’t catch on with a team. After playing in Europe, he returned home to Texas and transitioned into a career at Dell computers.

“Basketball wasn’t the main focus,” Jarrett Allen said of his childhood. “For my dad, he played his whole life. His life revolved around it. He just wanted us to be normal kids.”

Growing up in Round Rock, Tex., Allen was blissfully unaware of the intensity of elite youth basketball. “I didn’t know about that whole crazy A.A.U. scene,” he said.

Allen and his older brother Leonard played basketball in church and community rec center leagues for fun. “We were clueless about organized basketball, at least on an elite level,” said his mother, Cheryl. “We didn’t even know it existed, and I’m glad we were oblivious to that world.”

Free from the demands of travel team sports, Allen pursued other interests. “Jarrett from an early age has always had an interest and curiosity about the world around him,” Cheryl Allen said. “That is why his transition to Brooklyn has been an easy one. I’d like to think that not starting elite basketball so young helped. He was able to be a kid as long as possible before becoming consumed by it, which unfortunately happens.”