The Jumbrotron had gone dark. The TD Garden stands were empty on Sunday evening, and arena employees were quietly cleaning up after the 18,000-odd full-throated patrons who’d recently exited the premises. But a few TV crews were scattered around the court, bright lights and microphones beaming talking heads across the country. The Celtics had just completed a shocking 108-83 win over LeBron James and the Cavaliers in Game 1 of the Eastern Conference finals. It was an outcome that demanded takes.

After he finished delivering some to the NBC Sports Boston viewing audience, Celtics legend-turned-broadcaster Cedric Maxwell took a moment by the deserted home bench to discuss one of the great conundrums of the 2017-18 NBA postseason: What happens when a surprising team’s best player is a self-effacing, defense-first big man? One who is consistently excellent, but doesn’t consistently produce excellent highlights. Who always seems to be in the right spot, but who you don’t always notice unless you make a point to look. Handsome, but not a trendsetter; quotable, but not memorably so.

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“I think Al [Horford] set the tone,” Maxwell said of Sunday’s blowout Celtics win. “And to me, he will set the tone for the series. Because if he wins that particular battle [with Kevin Love], I think the Celtics will win the series. Because you’re not gonna stop LeBron James, not for a seven-game series. But what you can do is try to contain him. It’s gonna be the other guys who’ll have to step forward.”

Until this postseason, Horford was perhaps the definition of an other guy. He may be the most underrated star player in the NBA today, and the only one knocked for it. A five-time All-Star, but one who may be thought of as much for being the last pick on his team as for undeniably earning a spot in the game in the first place. He’s averaging 14.2 points, 8.6 rebounds, 3.2 assists, and 1.2 blocks a game in his 11-year career. His averages went down in the 2017-18 regular season, his first next to Kyrie Irving and second in Boston, yet he may be having his biggest impact.

“Absolutely he has gone up to another level this year,” Maxwell said. “And it’s because he knows his team needs him. He was going to be the guy who was going to be riding with Kyrie and making sure that [Gordon] Hayward got positioning to shoot. He was gonna be that other factor. Now he’s thrown in there as that key guy. That’s why he’s raised his game.”

“Everyone wants to know embarrassing stories, and I’m like, ‘Al, honestly, really always had his stuff together.’ And if he didn’t, he was very good at hiding it.” —Anna Horford, Al’s sister

That game was on full display early in Sunday’s contest. With the score tied at 7, Horford finished or assisted on five of the next six Celtics possessions. He found Terry Rozier open for a short jumper. He caught the ball on the block against Love, spun baseline and made a reverse layup. A couple of possessions later, Jaylen Brown drove into the lane and threw it up for Horford, who caught, gathered, and scored. Later, Horford got open for a top-of-the-key 3. Swish. Horford doubled LeBron after a switch put Rozier on the Cavs star, and when James passed cross-court to an open J.R. Smith, the big man sprinted from the free throw line to the 3-point line to close out, contributing to a miss. On the other end, the Celtics funnelled the ball right back to Horford, who attacked Love’s closeout with a drive, scored, drew the foul, and completed the and-1.

In roughly three and a half minutes of game time, the score was Horford 10, Cleveland 0. The Cavs didn’t get closer than 12 the rest of the way, and trailed by as many as 29.

Horford was a plus-17, finishing with 20 points, on 8-for-10 shooting, four rebounds, six assists, and two blocks. With Boston in control, he didn’t play in the fourth quarter.

So why, after the game, were all the takes ancillary to Horford at best? Maybe it’s because he makes his biggest impact on the Celtics’ league-leading, physical, and switch-heavy defense, with opponents shooting 5.9 points per 100 possessions better when he’s off the court in the postseason.

“I think Al Horford may be one of the most underrated players around,” Maxwell said. “I would say Al Horford, he’s vanilla. He’s not tutti-frutti. He’s not all these other flavors of the month. He’s just plain vanilla, and he’s good and solid. Because of that, I don’t think that he has that [wow factor]. ... He doesn’t ooh-and-ahh people, but he just gets the job done.”

And that is the story of Al Horford, star player: Even when the intent is to compliment Horford, people just seem to manage to throw more shade on him.

“Everyone wants to know embarrassing stories,” said Anna Horford, Al’s 25-year-old sister, “and I’m like, ‘Al, honestly, really always had his stuff together.’ And if he didn’t, he was very good at hiding it.”

Growing up the oldest of five siblings, Al was always there to offer words of encouragement and reminders that you get what you work for. As his basketball career progressed, Anna watched him adopt that same role with the Florida Gators, the Atlanta Hawks, and now the Boston Celtics. “I think he’s kind of taken the initiative and has been someone to look up to his whole, entire life,” she said.

Matt Herring, the Florida strength and conditioning coordinator during Horford’s three-year stint in Gainesville, said that “He was definitely the leader of that group, but not the vocal, outgoing presence that Joakim Noah was, and not the big, charismatic smile that Corey Brewer was.” He was the yin to their yang, showing an ability even as a college kid to ensure teammates kept their focus on the task at hand.

“Guys would follow him,” Herring said. “He could approach Coach [Billy] Donovan and talk to Coach Donovan about things. ... We knew that if Al brought us something, whether it was thoughts on the team or something [else], that it was coming from a very thought-out place. ... And we knew this was something we needed to listen to and address.”

Ask whether Horford’s low-key, workmanlike manner leads to him being overlooked, and those close to him are prone to bristling, Anna especially.

“It’s something that you’d think people would admire and kind of respect, but it also works against him,” Anna said. “Because people love the nitty-gritty, people love Draymond [Green] trash-talking. People love how LeBron James comes off as kind of cocky, and, I mean, he’s the best player in world.

“But Al’s not like that. He’s not narcissistic. He’s not selfish. I do think that kind of works against him. It’s not necessarily that people don’t like him. I think it’s that people aren’t as intrigued by him.”

Though Anna’s not above needling him about compliments on his eyelashes or asking him about the secret to his skin-care regimen (soap and water, he deadpanned recently) on her podcast, the Horford Happy Hour, she’s her brother’s biggest defender.The way she looks at it, someone’s gotta do it.

“I think Al Horford may be one of the most underrated players around. I would say Al Horford, he’s vanilla. He’s not tutti-frutti. He’s not all these other flavors of the month. He’s just plain vanilla, and he’s good and solid.” —Celtics broadcaster Cedric Maxwell

“The recognition is just something that he could not care less about. He just wants to win and contribute,” she said. “My thing is, ‘You may not like him but you should respect him and his game.’ … I see someone that I’m really proud of, and someone that our family is really proud of. And someone who’s made a significant impact on every team he’s ever been on, from the Gators winning two national championships, to going to the playoffs in every season in Atlanta, to doing great things in Boston.

“For him to not get the recognition, definitely bugs us more than it does him.”

Horford’s much more concerned with his work for the Celtics, which continues with Tuesday night’s Game 2, and—this will shock you—setting a good example for his young family. He and his wife, Amelia Vega, have two children, son Ean and daughter Alia, with a third on the way. The Horfords recently appeared in a spot for the NBA’s collaboration with Lean In, in support of gender equality at home and work, and Horford has helped rehab basketball courts and fund scholarships in his native Dominican Republic, in an effort to give kids on the island a chance he didn’t have.

His father, Tito, was the first Dominican to play in the NBA. And in a baseball-mad country, Al Horford has made a name for himself and inspired future generations of Dominican kids in the process. That includes Minnesota Timberwolves unicorn Karl-Anthony Towns, who plays for the Dominican national team. Towns told Sports Illustrated’s Andrew Sharp in 2016 that growing up, “I wanted to be the next Al Horford. And I told Al that, to his face.”

Horford was tired, but the work wasn’t done yet. Players know the game doesn’t end when the final buzzer sounds. The real end comes after the final quote is recorded, the final mic is turned off.

Horford’s a reliable quote, if not one to make stop-the-presses proclamations. So after the Celtics ousted the Sixers in Game 5 of the semifinals, it was a welcome sight when the Florida product took the podium alongside Jaylen Brown. But when he was asked to look ahead to Cleveland, the vet deflected the question in such a way as to disarm an at-times-prickly audience.

“I’m just happy we won tonight. It was a taxing game for us, we left it all out there. And I’m gonna be completely honest with you,” Horford said, “I can’t think about anything else right now. I’m very proud of our group. Our guys really fought.”

When the media members looked to Brown, sitting beside him, for his take, the second-year forward went to Horford for an assist. “Uh, yeah, I second everything he just said,” Brown said, drawing laughter. It’s not the first time Brown’s leaned on Boston’s dependable big man.

“It’s been a true pleasure on a daily basis,” Brown said of learning from Horford. “Everybody knows Al does everything the right way. [Even] if [things don’t] go his way, he always carries himself with a great demeanor. ... I learned a lot and will continue to learn a lot, on and off the floor.”

“He is that grandfather that you’re going, ‘Oh, man, I’m going to grandpa’s house and I can do this stuff.’ Al is that guy that they’re taking lessons from.” —Cedric Maxwell

When Horford signed a four-year, $113 million deal with Boston in 2016, he was supposed to be an elite-level complementary piece. The real prize that offseason was Kevin Durant, whom the Celtics thought they had a real shot at before he decamped from OKC to SFO. So instead of Durant, Horford, and Isaiah Thomas, the core became Horford and IT—the former a reliable 15-8 guy who had struggled to get the Hawks over the top in the postseason, the latter an unproven score-first point guard who had struggled to get a team to buy into his talent.

“[Horford’s] one of those guys that has won over and over. Wherever he’s gone, the team has won,” Maxwell said. The Celtics did just that last season, winning 53 games and making it to the Eastern Conference finals against the Cavs. Of course, Horford wasn’t the story of that season. He wasn’t the one being called “King in the Fourth,” or talking about Brink’s trucks. And when IT finally succumbed to his hip injury, the Celtics folded.

That’s the kind of supposed shortcoming his critics, those who seem to delight in labeling him “Average Al,” consistently hold against him. When your big selling points are defense, leadership, and showing up every day, people tend to notice any lapses.

Sometimes Horford seems like the sunrise in a cloudy city, dependably, undeniably brightening the landscape, and occasionally taking your breath away.

When Brad Stevens talks about Horford, he has a tendency to start smiling. Like he’s in awe, like he can’t believe his good fortune. You’d say he looks like a kid in a candy store, if he didn’t look like the kind of person who’d pick an apple over a chocolate bar.

It’s not hard to figure out why Stevens has that reaction. Sunday, Horford stepped up whenever the Celtics needed to answer a Cleveland run. In the second quarter, he scored on one end, then stayed with Jordan Clarkson on a drive, perfectly timing his leap to meet the lofted layup attempt and swat it into the crowd. The big man stared into the crowd after the block, coming as close to a strut as ever.

“I think that anybody gets a guy like that—that’s so solid, that understands the game, understands the nuances of the game—you’re gonna ride with him,” Maxwell said. “And I think Brad Stevens would have to be happy about that.”

“Al’s important to everything we do,” Stevens said after Game 1. “Every minute of every day, whether it’s the walk-through before, the meeting before, yesterday’s practice, yesterday’s film session. Again, he’s kind of our stabilizer and the guy that we all look to. And we take great comfort that he’s on our team.

“He’s our rock. He’s the guy we really, really lean on.”

Great, first he’s vanilla, and now he’s a rock. Horford is top-four in four of eight “hustle” stats during the playoffs, according to NBA.com/Stats, and he’s averaging 17.2 points, 8.3 rebounds, 3.5 assists, and 1.4 blocks per game. He’s forcing Cavs coach Tyronn Lue, a former teammate in Atlanta, to consider inserting Tristan Thompson into the starting lineup in an attempt to slow him down.

What other accidental shade can we throw Horford’s way before he has another chance to impress in Game 2?

“He is that grandfather that you’re going, ‘Oh, man, I’m going to grandpa’s house and I can do this stuff.’ Al is that guy that they’re taking lessons from,” Maxwell said. “He conducts himself as a professional, all the time. He plays hard out on the floor. I think if you’re a younger player, you emulate that, you’re gonna emulate some greatness.”