Marcus Smart doesn't take his eyes off the court. Not once.

Seated under the basket, he's polite—warm, even—in answering questions on this February morning. But a faint scowl lines his face. Not in a rude way. In a how can you stare at a court and not want to tear it up? kind of way.

It's 10 minutes before shootaround. Nine hours until the Celtics play the Cavaliers in Cleveland. But when Smart is near a court, he loses track of time. Loses himself between the lines.

Enough talking. He'd fly off his chair right now and chase down a loose ball if he could.

Screw his knees. His ankles. His arms. His back. Any ligament or joint in his body, really. If a ball is rolling, Smart is diving. He does it so often in games, you wonder if he popped out of the womb with his arms stuck straight ahead, instinctively ready to chase down a basketball.

He runs a three-man weave or a shell drill in practice like it's Game 7 of the Eastern Conference Finals. He warms up like he will lose his contract if his high knees aren't high enough, his butt kicks not quick enough. Even off the court, he can't turn off. One of his favorite hobbies is rapping, but instead of rhyming in the comfort of his home, he books studio sessions.

He has to push himself. Has to perform. He needs some sort of pressure.

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Even on this day, with the Celtics having won nine of 10 (part of a stretch that is now at 27-11 since their 10-10 start) and preparing for the lowly Cavs, Smart can't take a second off. He doesn't know how to. As his teammates chatter and take in their pregame meals later, about an hour before game time, Smart can be found in the center of the locker room, bending low, sliding side to side as a large resistance band hugs his ankles.

He doesn't drop his head. Doesn't unlock his tightly gripped hands. Doesn't take a peek at the grilled chicken, rigatoni pasta, roasted potatoes, honey balsamic salmon, peanut butter and jelly sandwiches or spinach salad sprawled across two tables to the left of him.

Just side to side. Side to side. The game has already started for him.

After it is over, after Boston pulls out a 103-96 win and thousands of fans scurry off into the cold night, something tugs at Smart. That absent presence. That painful reminder of the way things were and the way things are.

"It's just different being here," says Phil Forte Sr., who is like family to Smart and the father of Smart's best friend and former high school and college teammate, Phil Forte. "It's strange, her not being here."

Smart grows quiet. The Fortes know him better than anyone. Since third grade, when the kid from Flower Mound, Texas, couldn't shoot a lick but would rather get punched in the stomach than give up on a play. He'd shoot, miss, grab the rebound, shoot, miss, grab the rebound, sometimes four times a possession and wind up with 18 boards at the buzzer.

The Fortes know Smart is still mourning the loss of his mother, Camellia Smart, who died of bone-marrow cancer at age 63 last September, right before the 2018-19 season started. Camellia used to like traveling to Cleveland to watch Smart. She liked playing the slot machines at nearby JACK Cleveland Casino. Usually came out ahead of her son at blackjack too.

Smart was a self-professed "Mama's Boy." Losing her was losing himself. Losing her was finding himself. It still is.

So much of who he is, is who she was. She taught him to be a team player, deflecting praise when someone would approach her and compliment Smart's game. No, no, no. It was really the post player's rebounding that brought us back into the game! She'd yell at Smart to play harder, especially when he committed turnovers or missed free throws. Come on now! You better make those! She was tough. In ninth grade, when Smart accidentally hit his head on a door while horsing around, as blood gushed everywhere, she wanted to give him the nine stitches he'd need right then and there.

Long after Smart jumped to the NBA, even after he signed his four-year, $52 million extension last summer, she'd still wear his old, tattered AAU tournament T-shirts. She never needed to be wealthy. And her arms held everything Smart needed: love, acceptance, faith. No matter how many people criticized his spotty jump shot, she believed in him and would tell him, "Shoot till you miss!"

He misses everything about her. The way she'd call him after every Celtics game she couldn't attend and tell him she loved him. And critique his game. The greens she cooked—how you could smell them from outside the front door. The way she'd remind him that no matter how much death struck their family, God is good, all the time.

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She reminded him that basketball, though it mattered like hell, though it put food on the table, was just a game. It was supposed to be fun. A shield from the outside. A space he could control. Maybe that's why he loves defense so much; he can always control how hard he plays.

"I know. It's strange without her," Smart says to Forte Sr. "It really is."

It does not surprise those closest to Smart that he is playing his best basketball of his career while enduring the toughest moment of his life. "There's no question that's not a coincidence," says the younger Forte. "That's been that kid's mindset: Every time something gets tough, something gets harder, he somehow rises."

He's had to, for his team. The Celtics have been anemic all year. One game, they're thriving; the next, they're wandering. Big wins, tough losses. Constant speculation about Kyrie Irving's future. Up-and-down play from Gordon Hayward in his comeback from injury and from young stars Jayson Tatum and Jaylen Brown in what was supposed to be their breakout seasons.

Smart has emerged as a key piece in keeping them on track through it all. It's no coincidence, either, that Nov. 26, when coach Brad Stevens reinserted Smart in the starting lineup, is the demarcation between the 10-10 start and the 27-11 stretch that followed.

He's even making more jump shots. Taking smarter, more efficient shots, he is shooting a career-best 40.2 percent from the field and 35.9 percent from three.

"The best thing that I can say about him is: He's been here five years, and all five years we've been a playoff team," Stevens says. "All five years, he's really, really added to winning, and that has never stopped. He's doing it at an even higher level.

"When he's on the court, people play better."

Some of that naturally tends to get lost in a league in which shooting is king and analytics are valorized. The players running the floor alongside Smart are the ones who appreciate his value the most. Appreciate the way he hounds players 1 through 5. The way the 6'4" guard leaps out of nowhere to block players six inches taller. The way he'll throw down against whoever, whenever, to defend his teammates no matter the ejection or fine. He has never walked through a team walk-through, never taken a second off in any drill.

"There's never a player that can play like that for 82 games, that's built for that mentally and physically as Marcus Smart," says Travis Ford, his former Oklahoma State coach, who now coaches St. Louis University.

He makes his teammates question their own hustle: Did I truly give everything I have in my body, do whatever is humanly possible, to get this win? "Seeing his effort every day drove me to be a better player not just on game nights but during practice," says former Celtics teammate Jae Crowder, who's now with the Jazz. "He's a guy you want to go to war with."

And a guy you don't want to go to war against. He smothers, annoys, irritates. Has long garnered a reputation for being a flopper.

"On the court, he looks like this complete assh--e," says Kenny Boren, Smart's former coach at Edmund S. Marcus High School. "I'll be honest, a lot of times he is—but off the court, he'll do anything for anybody."

Ask any of his Celtics teammates their favorite Marcus Smart story—the most intense, most wild, most Marcus thing they've seen him do—and expect them to pause for two minutes and make you wait. It's not because they can't think of one; it's because they are flooded with dozens, since he brings that tenacity every day.

Like the time he drew two critical offensive fouls on James Harden in the final 7.3 seconds to steal a win in 2017. "Probably the craziest s--t I've ever seen," says Celtics forward Marcus Morris. "Even without the ball, he changes the game."

Like when he dove after a loose ball 30 seconds after checking into Game 5 of a first-round series against the Bucks in 2018. He didn't care that he had a splint on his right thumb, that this was his first game in six weeks after undergoing UCL surgery. He needed that ball and knocked it loose.

"I've been in TD Garden when it's electric. A lot," Stevens says. "I don't know if I've ever felt it like that, in that moment."

That makes him a fan favorite, because he's everything Bostonians are: Gritty. No nonsense, no patience. Not here for a gold star. A throwback player to his core.

"Back in the '60s, '70s, my mindset and the way I play would be perfect. They play like that every game," Smart says.

That's just what it is.

"That's just what it is! Exactly!" he says, a smile breaking through. "I think we kind of lost that in today's game. Everything's become real cute. Everybody's scared to go to the rim. Everybody's scared to get hit. Everybody's scared to touch.

"I thrive on the contact. Contact is in my nature."

Smart is only 24. It's easy to forget that when watching him or talking to him. He's one of those people who seem like they've lived four, five lives already. He has seen more, endured more. In his four-plus years in the league, Smart has evolved, matured, quietly. It's not that the game has slowed down for him. It's that he understands it more. Understands himself more. He looks comfortable. More than he ever has.

And yet he hasn't been selected for an All-NBA defensive team yet. A part of him does want to prove anyone who doubts him wrong, but he isn't motivated by accolades.

"It's about winning," Smart says. "A lot of this stuff, it's a popularity contest. … That doesn't determine the type of defender I am. That doesn't mean that I'm a bad defender. That doesn't mean that I'm not a great defender. It just means that some people like others more than others."

"I know who I am," he adds. "As a player, as a person, and what I can do. I'm not gonna change that for anybody."

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So he continues to slide, side to side, spilling his heart onto the floor. His passion overflows. Resists boundaries. It's electrifying, unifying. But sometimes it's been too much. Sometimes it's been to his own detriment. To his team's.

His mom always told him, "Never back down from a battle, but know how to pick the right ones."

That, he had to learn.

Forte Sr. saved a tiny piece of glass, about three inches tall. He stores it in a little bottle and shows it to Smart from time to time to remember.

To remember when this little piece bloodied Smart's hand and nearly ruined his career. To remember how special it is to play basketball for a living, to be a key piece for the Celtics. To remember when he was not able to control his emotions, those things that make him so exciting on the court but pulled him off it for two weeks.

Around this time last year, following a one-point loss to the Lakers in which Smart launched an ill-advised three as time expired, he returned to the team's Beverly Hills hotel and punched a picture frame in the bathroom. The glass broke through his skin and almost struck two tendons that ran along his pinky area. It could have ended his season or potentially even hobbled his career.

"What do you need me do?" Forte Sr. remembers asking when Smart called him in the ambulance on the way to the hospital.

"I just need you to tell me it's gonna be OK," Smart said between tears.

"It's gonna be OK," Forte said. "It's gonna be OK."

Smart felt embarrassed. Disappointed in himself. It all happened so fast. If he could have stopped his hand from diving into the frame, he would have. But he didn't. He couldn't. Not in the heat of the moment. He felt hurt, not because of what it did to his hand but because of what it did to his team. Missing time on the court ate at him.

"That kind of woke him up, noticing what it's like to have the game potentially being taken away from you," the younger Forte says, adding, "I think he just reached a point where he was like, 'I need to grow up a little bit.'"

That thought clicked in ways it had not earlier in his career, when he was unable to cool his competitiveness.

In high school, he once cussed out his high school coaches for calling him "out" during a kickball game. As a result, Smart's team lost the game. "That's f--king bulls--t!"he screamed in the hallway.

While playing for Oklahoma State, he was labeled a loose cannon. Uncontrollable. Especially after one Texas Tech game, when he fell into the stands in the final seconds of a loss and shoved a fan who was taunting him.

Few outside his team or his inner circle knew what he was dealing with at the time. His mom had been in the hospital. Ford says he was dealing with a lot that week. "It was a split-second reaction of a lot of different things," Ford says. "Was he wrong for doing it? Yes. But there was a lot more behind it than just that. … I knew what he was going through."

The struggles continued in the NBA. So did the ejections, the fines. He was so frustrated after a loss against the Washington Wizards in 2017 that he punched a hole in the visiting locker room wall.

"When he first came into the league, he didn't know how to channel his emotions, his passion," Crowder says. "He had to get better with knowing how to approach teammates, too, in a way during the heat of the battle."

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Learning to dial back was difficult. He didn't know any other way. Didn't know if he could be as productive—as captivating—without the fire that makes him him.But, as it went his whole life, those who criticized him only saw the hard, sharp parts of him. They didn't bother to look underneath.

When Smart is around kids, the tough guy melts. Disappears. Turns giddy. He enjoys coaching kids. One summer, he and some other Celtics players were at the University of Miami for the basketball camps of Hurricanes head coach Jim Larranaga, the father of C's assistant coach Jay Larranaga, and they were working out during lunch. Smart was shooting corner threes when the campers sneaked back in to get a glimpse of him.

"Mar-cus! Mar-cus! Mar-cus!" the kids began to chant.

A giant smile washed over Smart's face. He swished a three and then ran toward the campers, completing a roundoff back handspring. Then he popped back up and gave high-fives to every kid. They swarmed him like he was a rockstar swooning backward into a concert crowd.

"He has a really big heart," says former Celtics teammate Jeff Green, who's now with the Wizards.

Smart is a goofball, often pulling pranks, cracking everyone up in the Celtics locker room. He gets more animated, more excited when his teammates make a shot than he does when he makes a shot.

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"A lot of people are like: 'Marcus crazy! Marcus mean!'" says Smart's former AAU coach, Vonzell Thomas, who now coaches at Smart's YGC36 AAU team. "I'm like, 'Marcus not mean at all.' The kid don't have a mean bone in his body until you cross him the wrong way."

"Other than that, he's one of the people you'd love being around."

His fire comes from having to survive every day, from not having anything given to him. Seeing those he loved struggle. Die. Like his older brother, Todd Westbrook, who died of leukemia in 2004 at age 33. Gunshots and sirens were the melody of Smart's childhood. Gangs and violence and drugs were around him. That created the person Marcus Smart. That created the player Marcus Smart.

The Celtics knew who Smart was, and knew who he could be, when they drafted him. Walter McCarty, a Celtics assistant coach from 2013 to 2018, remembers interviewing Smart at the draft combine in 2014. He remembers Smart as personable, always smiling.

He knew Smart could be special. He was intelligent, able to make split-second decisions of when to close out, able to know exactly where opponents were looking to pass to get a deflection. "He's going to do everything he can to win," says McCarty, now the head coach at University of Evansville.

That is how his first few weeks in the NBA went. The first time Smart walked into the Celtics weight room to meet Bryan Doo, the team's strength and conditioning coach from 2003 to 2017, he brought his mom.

"Hey, so you're B-Doo, right? You stay on him," Doo remembers Camellia saying.

"I hear you're the one who takes young kids and does all this stuff that teaches them how to be men," she said. "Well, you better tell me if this boy isn't doing as he's told! Marcus, you hear that?!"

"Yes, Mama. Yes, Mama," he replied.

Doo quickly saw that Smart needed everything to be a competition. A challenge. A game. It wasn't enough to participate in Doo's warm-up conditioning drill of kicking a soccer ball a certain number of times. Smart had to exceed that number. "He just has another level to his game that other people can't go," Doo says.

Smart's basketball IQ shone early. "He was the most advanced young defender I've ever coached," Stevens says.

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But it didn't all come naturally for him. Smart struggled to embrace the monotonous parts of being a professional early in his career, like having a routine. Eating right. Some called him overweight. He was eating whatever he wanted, just like he did in college, often pizza and wings.

If he wanted to stay on the floor, his habits had to change. "It's hard to get here, but it's harder to stay," Smart says. "You gotta adjust. Physically, mentally, emotionally, psychologically."

Midway through the 2016-17 season, Smart told Larranaga, when the two first started working more closely together: "I just want to be held accountable."

Larranaga was impressed that Smart had enough humility to recognize that he needed to adapt, needed to be more consistent. Smart also hired a chef. He followed a more consistent fitness routine. He fired dozens and dozens of jump shots.

"Marcus is one of the greatest competitors there is in the world, in any sport," Larranaga says. "And a lot of times when you live for competition and you live for the game, it's hard to embrace all of the boring preparation and practice and the monotony of preparation. He's really grown in that area."

He was inching closer to the player he wanted to become—and showed it against LeBron James and the Cavs in Game 3 of the Eastern Conference Finals in 2017. He drilled seven threes en route to a career-high 27 points to lift Boston to victory.

"I think he kind of found his identity then," says former Oklahoma State teammate Kamari Murphy, now with the G League's Long Island Nets. "That gave him confidence. Around that time he kind of found himself, told himself he belonged there."

This season, Smart has become himself. But better. Just as fiery but more composed. More mature.

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He got ejected and fined $35,000 for charging at Atlanta's DeAndre' Bembry. But he was also the one to break up a disagreement between teammates Jaylen Brown and Marcus Morris.

He shot 42.9 percent on threes in January. Then he had a spell where he missed 20 straight in February. Then he followed that with a monster dunk late in the fourth quarter that iced a win over the Sixers to get the Celtics back on track after back-to-back losses in Los Angeles.

And all this in the middle of mourning. Well, not in the middle. There is no beginning, middle, end for this.

Never back down from a battle, but know how to pick the right ones.

"We love Marcus for who he is," Stevens says. "The passion to make the next right play, to show up every night to do his job, to do things that never get talked about or enter a stat sheet.

"Part of his growth is, he's understanding when to hit home runs on the court—but also how to react. Those are things that people benefit from with time and age."

And from not taking their eyes off the court for one second.

Mirin Fader is a writer-at-large for B/R Mag. She's written for the Orange County Register, espnW.com, SI.com and SLAM. Her work has been honored by the U.S. Basketball Writers Association, the Football Writers Association of America and the Los Angeles Press Club. Follow her on Twitter: @MirinFader.