His posterior became such a force in the front court that it assumed an almost anthropomorphic quality, as if it possessed an identity distinct from Sullinger himself. It inspired a Twitter account, for instance. The tag line: “Clearin room in the paint since 1992 with a greater gravitational pull than Jupiter.”

Between his freshman and sophomore years at Ohio State University, Sullinger, seeking greater mobility, dropped 20 pounds and cut his body-fat percentage. But not to worry, he reassured Buckeyes fans at the time. “I didn’t lose my best friend.”

As Sullinger prepared for an NBA career, though, another part of his body was drawing notice, this time unfavorably. A troublesome back, which had sidelined him for a couple of games at Ohio State, gave pro teams pause. A leading prospect before the 2012 draft, his stock dropped after NBA doctors flagged him as a potential injury concern. Teams with the highest picks passed him over, wary of investing in a risk. As a result, one of the most promising arrivals to professional basketball was still available when the Boston Celtics’ turn came, at pick No. 21.

The Celtics jumped. Danny Ainge, the team’s president of basketball operations, and coach Doc Rivers believed Sullinger was worth the gamble, even as Ainge allowed that he might need surgery at some point. One sportswriter called Sullinger “the steal of this draft.” Sullinger’s agent, David Falk, told me, “In essence, the Celtics were able to draft a player at 21 that I think should have gone No. 5. It was Christmas in June.”

That’s how Sullinger and his family felt, too. They were thrilled at his joining one of the NBA’s most storied and respected organizations, even if the lower slot meant a lower salary. “If you consider me landing to the Boston Celtics a drop,” Sullinger said at the time, “then I’ll do it all over again without a hesitation.”

Sully, as he is known, integrated quickly for the 2012-2013 season, even cracking the Celtics’ starting lineup. He became a bright spot on a squad that struggled early to find its form, scoring 16 points in two games in 2012 and grabbing 16 rebounds against the Phoenix Suns in early January. Then, in the first quarter of a January 30 game with the Sacramento Kings at TD Garden, Sullinger landed awkwardly after collecting a rebound. He hobbled off the court with back spasms and never returned.

At first, he figured he just needed a few games off. He received an epidural for the pain, which didn’t help. He knew that meant trouble. The morning after the game, a Thursday, he could hardly walk. The next day, Sullinger underwent season-ending surgery at New England Baptist Hospital to remove two herniated disks. “It was an emergency,” he explained to Celtics fans in a video chat on the team’s website almost two weeks later. “I was in so much pain.”

The injury was bad news for the Celtics, and at a bad time. Over the course of 16 days, the team would lose three players for the season: Sullinger, all-star Rajon Rondo, and guard Leandro Barbosa. The team had always known surgery was probable for Sullinger, Rivers told reporters; they’d just hoped it wouldn’t come in the middle of the season.

You could almost hear last summer’s skeptics clucking: See, we knew his back was a problem. Here’s the thing, though. Three months of the season was enough for Sullinger to show what he could do. He impressed the Celtics, its fandom, and players on rival teams with his poise, sticky hands, and willingness to learn. “His feel for a rookie is unbelievable, his feel for the game,” Rivers tells me. “You don’t see that in rookies — the patience and the pace that he plays in.”