WALTHAM, Mass. — The practice court was cluttered with TV cameras, soft white lights, tripods of all shapes and lengths and wires sprawled everywhere across the parquet floor.

For this one day the equipment of the back stage had been moved to center stage as Al Horford sat in a corner of the crowded gym that will be his new basketball home.

It might have been an overwhelming first day if not for the banners.

“I’m very aware of them,” Horford said Monday at Celtics media day. “I’m not going to lie to you, the first time I was here (as a visiting rookie) I couldn’t stop looking at the banners up top. I couldn’t stop looking at them. It’s something that’s powerful.”

Now the perspective had changed. After nine seasons in Atlanta, Horford signed a four-year, $113 million contract with the Celtics. Now the banners have become a grounding influence.

“I have a good idea of the history and the passion of the people here,” Horford said. “This is a special place, a lot of expectations, and I’m excited.”

Horford has never played in an environment so passionate as this one. Starting Tuesday, and for every day thereafter at practices or games in Boston, Horford will be reminded of why he and the Celtics were so deeply interested in one another last summer. His new fans will be expecting him to improve an unfinished young team that won 48 games before falling to Horford’s Hawks in the opening round.

“We have some great leaders here already,” Horford said. “I want to be able to help our team grow, get acclimated as fast as I can, and just help us be a better team. I want us to grow. I took a chance on coming here, and I believe in the guys we have here, the organization, and the potential that there is here.”

As Horford looked back on his six-game victory over the Celtics last postseason, he recognized that the city had already started to recruit him.

“I try not to pay attention to a lot of it, because you know the fans here, they’re pretty intense,” Horford said. “But I did notice the fans would say, ‘You’re going to be here next year.’ I did notice the people weren’t coming at me like in the past. They are a very smart fan base, and they cut me a break, I think they did.”

“He’s going to help us so much in so many ways,” said All-Star guard Isaiah Thomas. “He’s so unselfish, not just offensively but defensively, and he’s somebody we need.”

“I love his experience, his character and his versatility,” said Celtics president Danny Ainge. “He fits into our system where we have the big guys handling the ball a lot.”

Though expectations have grown, Ainge and coach Brad Stevens both discussed improvement in terms of an open-ended way. “Being better the next day, that’s my perspective,” said Stevens.

A preliminary goal, clearly, is to win a playoff series for the first time since 2012. “All offseason that’s all I thought about,” said Thomas. “Losing that series (last year) left a bad taste in all of our mouths. I want to win a playoff series, go further. Last season hurt me because for the first time I could say in my life I gave everything I had — that’s why it hurt so much. I had nothing left in me. We’re looking for bigger and better things. What that might be, I don’t know … just getting to the playoffs in Boston isn’t good enough.”

“We have a lot of guys not yet in their prime and I do expect them to be better,” Ainge said. “We want to be better at the end of the year than we are at the beginning, and we want to be able to compete against the best teams. We’re not going to be able to sneak up on anybody. I think the team has earned a great deal of respect, the way they’ve played. Living up to those expectations is part of growing.”

The four-time All-Star is an upgrade over Jared Sullinger, the young power forward who moved onto Toronto last summer. But Horford won’t mitigate another departure from Boston — the ballhandling loss of 6-foot-7 Evan Turner, a secondary point guard who was at his best making big plays in the final minutes. Before he signed last summer with Portland, Turner was a classic Celtic in this sense: He had the talent of the No. 2 pick of the 2010 Draft, and yet he didn’t mind coming off the bench or averaging a scant 10.5 points so long as he was contributing. If the Celtics struggle, a root cause may be the absence of Turner down the stretch in tight games.

Horford addresses a different need. Boston hasn’t had a notable big man since the departure of Kevin Garnett, an Obi-Wan figure who continues to provide — even now, in his Celtics after-life, he promises to strengthen Boston by way of the draft picks he (with Paul Pierce and Jason Terry) elicited from Brooklyn.

Like Garnett, the 6-foot-10 Horford is an excellent shooter who prefers the perimeter to the post. But he will not be the transformative force that Garnett was. Instead, Horford is meant to help the Celtics continue on their current path. He will be a constructive leader who sees things from the point of view of his younger teammates, and a selfless scorer who should improve the offense without reinventing it. He ought to fit right in.

What the Celtics still need to complement Horford is a rim-protecting center who can also provide a scoring presence in the post. In the coming months the Celtics can be expected to continue trade talks with Philadelphia, who are likely to move either Nerlens Noel or Jahlil Okafor regardless of Joel Embiid’s recovery.

The identity of the Celtics will continue to be established by their wing defenders who are just now realizing how good they can be. Avery Bradley, 25, is talking about earning defensive player of the year. A breakout season is anticipated of third-year year point guard Marcus Smart. Jae Crowder, whose defense and 3-point range are coveted by many teams, is only 26.

Rookie Jaylen Brown, the surprise No. 3 pick overall, figures to earn minutes with his defense. His body and athleticism are NBA-ready, even if his shooting and decisionmaking need work at age 19.

Horford’s reliability as a 3-point shooter will address another need, though it would also be helpful for second-year shooting guard R.J. Hunter to provide steady minutes from the arc. The Celtics were among the worst 3-point teams last season.

The oldest Celtics are Horford and backup swingman Gerald Green, both 30. The youth of their teammates has much to do with the cost-efficiency of Boston’s roster. There isn’t a bad contract on the payroll. Thomas and Bradley won’t be free agents until 2018, and most of the young core can remain on rookie contracts through next season. All of those relatively small salaries will enable Boston to continue utilizing a deep high-energy rotation to build up the value of its players in pursuit of a blockbuster trade over these next two seasons.

“I have not accepted that yet,” said Ainge when asked if a championship is beyond reach of his young team. “I have not accepted that.”

In other words, Ainge is going to continue seeking a star who could elevate Boston to contention.

“Everybody seems to be on the same page on when to pull the trigger on a deal and when not to pull the trigger,” said Ainge. “We’ll be in that position for a while. We have a lot of assets, a lot of young players and we like all of our young players.”

Ian Thomsen has covered the NBA since 2000. You can e-mail him here or follow him on Twitter.

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