ONCE AGAIN, BRIAN SCALABRINE finds himself on a court working on his game. But this time, instead of a basketball, he’s holding a racket and trying to hit a tiny rubber ball that barely bounces. Since being elbowed into retirement last year, the 11-year NBA veteran whose popularity has long dwarfed his playing time has taken up an unlikely sport: squash.

On this January morning, the 6-foot-9-inch Scalabrine is in the middle of very small tempered-glass enclosure at the ritzy Tennis and Racquet Club on Boylston Street. He’s dripping with sweat, dashing back and forth across the court with enormous strides. He’s playing hard — and losing. In fairness, his opponent is Shahid Zaman Khan, the club’s 5-foot-8-inch resident pro, a scion of a Pakistani squash dynasty who was once ranked the 14th best player on the planet. Scalabrine picked up the sport less than a year ago.


Squash is a small but important part of the new Brian Scalabrine Game Plan. The ex-Celtic has reached the place where all pro athletes someday find themselves, aged out of the sport to which they devoted everything, yet with their whole lives still ahead of them. Some lose their shirts to hangers-on and poker tables; others slip into a quiet retirement, spending weeks on golf courses or the beaches of Bermuda. Not 34-year-old Scalabrine, who’s both too smart to blow his millions and too antsy to sit still for long.

Instead, he moved back to his home state of Washington, where he lives just outside Seattle with his wife and two young daughters. He still plays hoops with friends, though it’s tough to find competition, and he bought a longboard. Skateboarding lets him work on his balance, he says, a point he underscores by bending his knees and stretching out his arms. For work, Scalabrine landed a broadcasting job with Comcast SportsNet New England, putting his gift of gab to use as an in-studio analyst and part-time commentator for Celtics road games. He was terrible in the beginning, as he’s the first to tell anyone, but he prepared hard, asked questions, and learned. This is how Scalabrine approaches every new challenge. This is the secret of Scal.


On the squash court, Khan scores another point. He’s now winning 5 to 1. Scalabrine lowers his racket and asks him a question. Like basketball, squash is a game of angles. Scalabrine sees those relationships on a basketball court, but some of the subtleties within this tiny space escape him. His strokes need work, and he frequently over-pursues the ball, chasing it too close to the back wall.

Unembarrassed by his struggles, he listens carefully as Khan explains how to hit a proper forehand. He learns fast. The next time Khan drives a ball to the back wall, Scalabrine returns the shot with noticeably improved form. It’s still not the prettiest thing in the world, but it gets the job done.

Story of his life.

***

NINETY MINUTES before the tip-off of the Christmas Day Celtics game against the Nets in Brooklyn, Scalabrine is the most popular man on the Barclays Center floor. As a woman who vaguely resembles Rihanna puts the Brooklynettes through their warm-ups, he chats with the Celtics’ assistant coaches, ESPN’s Chris Broussard, players from both teams, and a steady stream of well-wishers.


Everyone, it seems, wants to talk to Scal, and he’s happy to oblige. When he signs an autograph for a kid in a Joe Johnson Nets uniform, the boy is ecstatic; his father perhaps even more so. “It’s amazing,” says Mike Gorman, Scalabrine’s partner on the Comcast broadcast. In Chicago a couple of weeks ago, Gorman adds, “he was more popular than Rahm Emanuel.”

Scalabrine wasn’t always a cult hero. After an unremarkable high school career — he was cut from his freshman team — he stepped up in junior college, then built himself into a bona fide star at the University of Southern California, leading the Trojans to their first March Madness victories in two decades. The New Jersey Nets picked him in the second round of the 2001 draft, though he was plagued by injuries before the season even started. After years of struggling to make an impact, he scored a career-high 6.3 points per game in 2004-2005, then parlayed that into a five-year, $15 million contract with the Celtics.

At first, Boston fans didn’t take to the big man making millions to warm the bench. The Garden would shake with mocking chants of his name. On the rare occasions when the Celtics were winning, people began to think of him as a human victory cigar — a guy you only put in when you’re 20 points up and there’s two minutes left on the clock.

But then something weird happened: Scalabrine won over the crowd. The chants grew fonder — and louder. He didn’t play a minute during the Celtics’ championship run in 2008, but he embodied the never-die attitude of that squad, cheering enthusiastically and revving up the crowds. He was still on the bench, but he was the Boston faithful’s guy on the bench. And during practice, his smarts and drive made the Big Three better. Kevin Garnett once called him the best teammate he ever had.


Scalabrine signed with Chicago after the 2009-2010 season and instantly became a fan favorite again. It was there he dubbed himself the “White Mamba,” a play on Kobe Bryant’s nickname, “Black Mamba.” The black mamba is the world’s deadliest snake, Scalabrine offered by way of explanation recently. “The white mamba is the world’s most dormant snake. It just chills. Watches and chills.”

Yet Scalabrine isn’t one to sit idly for long. Immediately after the Bulls lost to the Philadelphia 76ers in the first round of the 2011-2012 playoffs, he sent Comcast SportsNet a message offering his services. The 76ers were playing the Celtics in the next round, he wrote, and he knew that team better than anyone.

When the following pre-season came around, Scalabrine didn’t get called back by the Bulls, or by anyone else in the NBA. (He did get an offer in Europe but didn’t want to leave his family.) He was a little surprised, maybe a little hurt, but also ready. “Part of what made me good as an athlete was the idea that this could be my last day as an athlete,” he says. “Having that in the back of your mind means there are always different things you can do to set yourself up.” Turning down an assistant coaching job with the Bulls — he wanted a stable schedule — he instead took the job with Comcast. “I was literally unemployed for one day,” he says proudly.


Back at the Barclays Center, a couple of buddies in the seventh row — both in their 20s, both redheaded — spot Scalabrine. “Scal,” yells one, “can we get a photo?” Scalabrine looks up and nods. The guys walk down, but a security guard stops them. Negotiations ensue about whether the guard should let them on the floor. “If you’re going to get fired, don’t do it,” Scalabrine tells him with genuine concern. The fans, turned away, ask Scalabrine to come up to them. “I got to work,” he says before turning back to the broadcast table. But a minute later, unwilling to disappoint, Scal’s back: “I’ll get you guys before the national anthem,” he calls out.

People loved Big Scal for the joy he brought to pro basketball, and they love him now for the same reason. But the happy-go-lucky exterior belies both how seriously he takes the sport and how good he is at it. “I always have fun, but I’m also very serious and extremely focused,” says Scalabrine, who has a tendency to talk as if he were still playing pro. “I live and die with the NBA. When you win, it feels so good, and when you lose, it feels so bad.”

Scalabrine’s USC coach saw this passion firsthand. “He was one of the worst guys to have around, because he just wanted to talk basketball all the time,” says Henry Bibby, now an assistant coach with the Grizzlies. “That would drive you crazy. Sometimes you just don’t want to talk about basketball, but he wanted to talk about basketball.”

Scalabrine never goofed around on the court, but he was happy to ham it up during TV and radio interviews. A kind of unintended corollary of that, though, made him seem like the one pro player every rec-league amateur was sure he could beat. Scalabrine says he doesn’t think people really know how good he is.

In mid-January, as a kind of reminder, Scalabrine competed in the “Scallenge” — one-on-one games against four talented Boston-area amateurs — an event organized by 98.5 The Sports Hub’s Toucher and Rich show. Scalabrine crushed each of his opponents. He scored a combined 44 points; they got only 6 (and a recently graduated member of the Syracuse men’s team put up half of them). Scalabrine played in 520 pro games, after all, shot millions of practice shots, and spent his afternoons going one-on-one with Paul Pierce.

Now Scalabrine brings his experience and work ethic to bear explaining basketball games to his television audience. Sitting courtside, he is talking about getting better as a commentator. Nearby, Rajon Rondo — Scalabrine’s immediate answer to the question, “Who would be the best squash player in the NBA?” — warms up, hoisting that ugly but increasingly effective one-handed jumper over and over again. “In broadcasting, it’s little things, tidbits, that paint a good story,’’ Scalabrine says. “I had to learn that. You have to realize what people want to hear.”

Gorman has watched Scalabrine evolve in the eyes of the fans. “The perception of him is an in-joke who sat down at the end of a lot of benches,” he says. “I think people are frankly stunned by how much he knows about the game and how much of an X’s-and-O’s guy he is.”

While Gorman and I talk, Scalabrine stands 10 feet away. He alternates between scanning a press packet stuffed with facts and figures related to the night’s game and chatting with a line of friends and well-wishers. Every once in a while, he’ll look over to the Celtics and Nets benches, sometimes for a little too long. “I’m excited about doing a good broadcast, but it’s not the same,” he’d told me earlier. “The highs and lows are so much smaller than when I was an NBA player.”

***

Benny the Bull, the mascot of the Chicago Bulls, held a sign behind the Celtic’s bench with a photo of former Celtic player Scalabrine. Getty Images/Getty

AFTER SCALABRINE and Khan wrap up their squash game — the pro wins easily — it’s my turn. I played in college, and minute by minute I can feel him get better as he grows more comfortable. His positioning improves; his sense of spacing gets sharper. Sure, he’ll never go pro, Khan even says as much, but that’s not what’s important now. Scal’s just happy for the challenge.

While it’s nearly impossible to find a pickup basketball game in which he’s not the best player on the court, squash offers Scalabrine an athletic pursuit that’s entirely new. He wears a huge smile when he recounts the time a few months back that he lost to a 12-year-old. It was a beatdown. And yet, despite the lopsided score, Scalabrine thought he played well. This kind of thing matters to him. “It’s great to play something where I have a lot of room for improvement,” he says.

In October, Scalabrine attended the US Open Squash Championship in Philadelphia. He describes watching Ramy Ashour, the world’s top-ranked player, with the same awed voice a teenager might use after watching LeBron James drain 3-pointers in warm-ups. Scalabrine has enormous respect for the effort it takes to go pro. He’s been there.

As for his squash game, Scalabrine has less ambitious goals than he did in his NBA career. He mostly hopes the ball goes in the right direction. He loves the workout of the game, which is chess to racquetball’s checkers, and how it keeps him moving and thinking constantly. “I feel like if I would have done this throughout my whole basketball career, I would have become a better player,” he says.

But those days are over. When Scalabrine plays squash, there’s no audience. No arena full of fans chanting “Scal-uh-bree-nee” until the rafters shake. But that doesn’t mean he’s ready to lose. Trailing 9-5 in a game to 11, he misses an easy shot. “C’mon, Brian!,” he admonishes himself. When Scalabrine gets on a court, he competes. It doesn’t matter if anyone’s watching.

Noah Davis, a freelance writer in Brooklyn, contributes to grantland.com and The Wall Street Journal. Send comments to magazine@globe.com.

WATCH THE VIDEO To see Scal on the squash court, click here.