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.”

IT WASN’T JARED SULLINGER ’S HEIGHT that established him as an imposing presence on the basketball court. Not his arms. Not speed. No, it was something else: his rear end. As a top high school prospect in Ohio and then an elite college player for two years, Sullinger skillfully employed his backside to carve out space under the hoop. Space to yank rebounds. Space to score from the post. Space to frustrate opposing big men.


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.”

No guarantees that Sullinger remains a Celtic, of course; owners of pro sports teams can be fickle in pursuit of success. But, having just celebrated his 21st birthday, Sullinger’s already being talked about as the heir apparent to Kevin Garnett, a.k.a. The Big Ticket, who turns 37 on May 19. Sullinger is wide. Garnett’s a walking razor blade. Sullinger loves to joke off the court. Garnett is notoriously, sometimes opaquely, intense. They are bonded, though, by a common motivation: a fierce desire to prove doubters wrong.

***

THE LINE OF PEOPLE snakes around the front of Goodwill headquarters in Roxbury. It’s a bitterly cold January evening, but they wait, most holding bags — black trash bags, white plastic bags with smiley faces, paper shopping bags — bulging with clothes. Several tons altogether.


Jared Sullinger, in gray sweat pants, black sneakers, and a black Polo sweat shirt, waves to the crowd and ducks inside, where he will spend a couple of hours handing out autographed pictures, chatting up eager fans, and posing for grip-and-grin photos. On the eve of what will be his final game of the season, he is here to help boost donations, which often ebb in winter. The clothing drive, which Sullinger initiated, is one of the first tests of his celebrity.

Some 600 people come out, including Elizabeth Huff of Londonderry, New Hampshire, and Eric Maxwell of Nashua. “He’s already made such a difference,” Huff, a 25-year-old medical assistant, says of Sullinger’s contribution to the Celtics. Maxwell, a 25-year-old accountant, says he hopes Sullinger develops into Garnett’s successor. Denise Jessamy, a 42-year-old fan from Dorchester, already feels protective. Citing a tussle in a recent game with the Miami Heat, she says, “I was ready to go down to the Garden and fight for him.”

Before greeting fans, Sullinger is led into a conference room to address teenagers in Goodwill’s Youth Initiative. He attempts a joke about girls and makeup, which lands a little flat, and then gets preachy. “Stay in school,” he tells them. “Do your homework.” It sounds like generic public-service-announcement stuff ripped from afternoon TV. But Sullinger has a reason for dispensing it.


He tells them the story: how, as a 15-year-old sophomore at Northland High School in Columbus, he screwed up big. This was 2008. A star on the top-ranked Northland basketball team, he was struggling in the classroom. He was put on academic probation. Unmoved by the warnings, he blew off his work for biology class. His basketball coach had seen enough, and he benched Sullinger for a big playoff game.

That coach was his father, James “Satch” Sullinger, a legend in Ohio high school basketball who held his players to high standards, on and off the court. His philosophy: “You play the game the way you live your life.” Jared tried to negotiate. His father didn’t budge. “I’ll be damned if he was going to turn that program into junk,” Satch Sullinger says now.

It was stunning, the father keeping the son out of such a consequential game. The son, after all, was already one of the top high school players in the country. Jared couldn’t believe it. “My body went into shock,” he told me. “I couldn’t move. I couldn’t speak.” But it got worse. With Jared in street clothes, Northland lost the game, crashing out of the state tournament. “It was a tough night,” says Trey Burke, a close friend and former Northland teammate who’s now a star sophomore guard at the University of Michigan.

The lesson Satch says he wanted to impart was this: “Don’t you ever treat something you love with disrespect again.” It worked. Jared rededicated himself to school. His work ethic improved. He learned what personal responsibility meant. “It’s just like it has cleansed my soul,” he said the next year, when Northland claimed the state title. That stain of failure — of letting his team and his city down, of being the face of disappointment on the front page of the local sports section — is still fresh.

This is why he’s lecturing teenagers at Goodwill on a cold Tuesday evening. “You don’t want that,” he tells them. “That’s the worst feeling ever.”

The story offers a glimpse into how Sullinger was raised, the youngest of three boys in a basketball-obsessed household. His older brothers, Julian and J.J., both played Division 1 college basketball. His mother, Barbara, a math teacher in Columbus, told Cleveland’s Plain Dealer that she had bought her sons blocks, trucks, and other toys when they were young, but “they didn’t want anything to do with anything unless it was round and bounced.”

Satch retired from coaching a couple of years ago, giving him more time to watch Jared amass an impressive 65-11 record at Ohio State and twice help lead the Buckeyes deep into the NCAA tournament. Satch plans to retire from teaching at Northland this spring, hoping to become a regional NBA scout. (A disclaimer is probably in order here: As a Columbus native now in Boston, I’ve rooted for Sullinger’s teams for a few years. Satch often holds court at the Starbucks down the street from my childhood home, a cup of Pike Place Roast in hand.)

There’s a paradox inherent in Sullinger’s coming-of-age. Even as scouts and sportswriters were naming him a top prospect, critics questioned his potential. He was too big or too slow. He wouldn’t make it at the college level. He wasn’t quite tall enough for his position. Even Rivers, who had watched a teenage Sullinger play against Rivers’s son, Austin, in competitive amateur games, once thought of Sullinger as the “fat, slow guy.” “Jared’s been trying to prove himself throughout his entire life,” says Aaron Craft, a junior standout on the Ohio State team who played alongside Sullinger for years. “He wants to prove people wrong and wants to show people how successful he can be with what he’s been given.”

Now Sullinger finds himself tested once again, determined to come back strong and help lead the Celtics into the future. I ask Satch whether it was hard, as a parent, to watch his son suffer a season-ending injury, just as he was starting to get traction. “What we want and what happens are two different things,” he says. The fortunate thing, he says, was that the surgery came after the Celtics already knew he could play. “Fate,” he says, “is God’s way of staying anonymous.”

***

WHEN SULLINGER FIRST joined the Celtics, one thing stood out in his reports back to friends and family: the education he was getting from Boston veterans. “He told me, ‘I’ve learned so much from guys like Kevin Garnett and Paul Pierce,’ ” says Ohio State head coach Thad Matta. “A lot of guys don’t want to go in there and learn.”

That humility, paired with a holistic sense of the game — both gifts from his upbringing — endeared him to his new teammates. “He brings a lot to the team,” says guard Avery Bradley. “Somebody that learns fast.” Another guard, Jason Terry, praises his “basketball IQ.” Jason Collins, whom the Celtics traded in February to the Washington Wizards, says Sullinger is capable of averaging a double-double (double figures in points and rebounds per game) in his NBA career.

Most notably, Sullinger has embraced the role of pupil under Garnett, one of his idols growing up and the man he may yet succeed. When Sullinger first moved to Boston last summer, he worried what playing under Garnett would be like. Would he get screamed at? Cussed out? Humiliated? “I was just mentally being prepared to not cry on the bench,” Sullinger told USA Today last November.

But Garnett took to him after seeing his desire to improve. “Me and Sully have a really good relationship,” he told the newspaper. When I ask Sullinger how he got in Garnett’s good graces, he says it was relatively simple. “You’ve just got to play basketball,” he says. “It reminded me of my father.”

Sullinger, listed at 6 feet 9 inches and 260 pounds, became, this season, one of the youngest starters ever for the Celtics. He’s still a rookie, though; indeed, Rook is one of his nicknames. He has had to fulfill rookie duties, like buying peanut butter and soap for the all-stars. As a newcomer, he drew frequent foul calls from NBA officials.

It was difficult, he says, to accept that back surgery would put a hold on everything. “But I’d rather have the surgery now than later in my career,” he says. Comments by Ainge and others suggest the Celtics feel the same way — that getting the surgery out of the way could prepare Sullinger for a prosperous future in Boston. As of February, the team expected him back for training camp for the 2013-2014 season. (Disk problems have slowed other prominent NBA players over the years, including Rivers himself and Larry Bird, who had surgery toward the end of his career on the court. More recently, Los Angeles Lakers center Dwight Howard has battled to return to top form after undergoing surgery on a herniated disk in the spring of 2012.)

The Celtics will need fresh legs. Pierce and Garnett don’t have many years left. Ray Allen, the third pillar of the Big Three, which brought Boston the 2008 NBA championship, left for the Miami Heat last year. In addition to Rondo, Avery Bradley, at 22, and forward Jeff Green, who is 26, are other young players who could figure largely in Boston’s future.

Those who know Sullinger say his personality, maturity, and “old-school values,” in the words of his agent, make him a good fit for the organization. “You like being on the floor with him,” says Chris Jent, an assistant coach at Ohio State who played for the Buckeyes and in the NBA. “He’s got a good way about him. It’s just fun to see kids like that be successful.”

After a while, Sullinger intends to finish his college degree, too. He doesn’t really have a choice. He promised his mom.

***

IF THERE’S ONE THING Sullinger has now, it’s time. Too much time. “I’m bored, people. I’m really, really bored,” he said in his video chat, explaining how he’s kept himself busy post-surgery. Netflix, for one. Video games, too: Call of Duty, Madden, Grand Theft Auto. He is on Twitter all the time (@Jared_Sully0).

His soundtrack features Jay-Z, T.I., and Nicki Minaj, but also poppier fare from Miley Cyrus and Carly Rae Jepsen. (Do Google his hilariously off-key rendition of Cyrus’s “Party in the USA.”) He has gone to games as a spectator, but, immediately after the surgery, had to watch some on TV. “I’m always at home yelling, screaming,” he said in the chat. As of late February, his pain was minimal, he was reasonably mobile — able to walk and drive — and he had not yet begun his rehab work.

Sullinger, adjusting to life away from Ohio for the first time, acknowledges he’s discovered next to nothing about Boston, having focused almost exclusively on his craft. When a fan asks on the chat about his favorite part about the city, his answer — TD Garden — is a bit pathetic, and he knows it. Yes, he admits, he needs to expand his horizons. When I ask him what he does for fun, he says, “I couldn’t tell you.” He does love what he’s seen of Boston, though. “People have open arms around here,” he says.

His father, meanwhile, is adjusting to life as the parent of an NBA rookie, helping where he can but also keeping a respectful distance. On a trip to Boston earlier this season, Satch asked his son if he could come along to a Celtics practice. “Jared said, ‘Oh no!’ ” Satch told The Columbus Dispatch. “He said, ‘There are no other dads there, and I’m not going to be the first one on the team to ask if his dad can come.’ ”

Satch says he has always told his sons to ask themselves what lesson God wants them to learn. For Jared, he says, “I think the lesson he’s learning now is patience and not taking things for granted.” It’s a lesson Satch believes his son will absorb, spurring him to get smarter about taking care of his body.

Before a recent Celtics practice, Pierce says Sullinger has shown the potential to return strong. But when I suggest Sullinger has already made his mark in Boston, Pierce pushes back a little. “In this league, you’ve got to continue to make your mark,” he says. “You don’t just play a few games and then, you know, ‘Celtic for life.’ You’ve always got to prove yourself. You’ve seen a lot of good players come and go. When he comes back he’s just got to make sure he’s in the best health he can be in and continue to make his mark.”

That’s just what Sullinger intends to do. “The way I was raised was to always push through tough times,” he says. “Everybody will always doubt me for who I am—being short, being tall, it doesn’t matter. But at the end of the day, I’ve got to keep pushing. It’s not about what they say. It’s about what I do.”

Scott Helman is a staff writer for the Globe Magazine. E-mail him at shelman@globe.com and follow him on Twitter @swhelman.