Fans came to watch Allen Iverson play in the “Big3″ Sunday in Brooklyn, but he spent most of his time on the sideline coaching. (Al Bello/Getty)

BROOKLYN, N.Y. — A grand experiment began here Sunday afternoon — at least, that’s how it was deemed by those who took part in it.

The Big3, a 3-on-3 basketball league created by Ice Cube and featuring former NBA players led by Hall of Famer Allen Iverson, made its debut here at Barclays Center Sunday afternoon, with four games featuring all eight of the league’s teams taking place over six hours in front of an announced crowd of 15,177.

“Outside of the NBA, this is the most competitive league in the world,” said Clyde Drexler, the coach of Power, which beat Tri State, 62-58, thanks to a game-winning three-pointer from 13-year NBA veteran DeShawn Stevenson.

“The Big3 is here to stay.”

That very much remains to be seen. The Big3 provides plenty of nostalgia, but those interested in quality basketball should look elsewhere. That’s why — at least in its current form — it seems the success of this venture will come down to nostalgia’s staying power.

Players and coaches gushed about the quality of play, but in truth, the participants looked like what they are: retired NBA players and journeymen. Play was stilted, with long scoreless stretches. Those led to games lasting more than an hour, even though a team must reach 60 points and have a two-point lead to win. Given the scoring system — featuring four-point shots from three spots that are more than 30 feet from the basket and a complicated system that makes some free throws worth one point and others worth two — the points should add up quickly.

That helps explain why the games will be broadcast on tape delay at 8 p.m. Monday on Fox Sports 1, as opposed to being shown live. Fans complained about this on social media Sunday, but given the length of the games — action began shortly after 1 p.m., and the last game finished more than six hours later — a live broadcast wasn’t feasible.

Then there was the injury factor — easily the biggest impediment to a league featuring players in their late 30s and 40s. Jason Williams went down in the first game with a noncontact right knee injury, eventually hobbling off under his own power. Corey Maggette was lost in the second game to a right knee injury, and after his team, Power, won on Stevenson’s three-pointer, Maggette hopped around the court on one leg to celebrate with his teammates before being helped off.

And, in the final game, Kenyon Martin was forced to sit with a hamstring injury after reaching for a loose ball — an injury Martin said he’d never suffered before in his life. Everyone involved, however, said age had nothing to do with these injuries.

“I just reached for the ball,” Martin said. “I did everything feasible to get loose … my normal routine that I’ve done for 15 years. It’s one of those things. Fifteen years playing in the league, I’ve never done this.

“It’s the same routine. Because of my age … it’s got nothing to do with that. Something happened. I reached wrong, and I pulled it. You know how many loose balls I’ve reached for in 15 years [in the NBA]? I’ve been playing basketball since I was 10 … I’ve never did this.

“So it’s got nothing to do with my age. It’s just one of them things, man. I’ll get ready to play next week.”

Of course, one would argue that age is exactly why they would be more susceptible to such injuries. Players are going to struggle to get as loose and play in the same way that they did in their mid-to-late 20s to mid-30s.

There’s no better example than Iverson. Since the league was unveiled in January, Iverson has been its face. In a video on the league’s website, Iverson prepares to play by working out with his high school coach, giving the impression he wouldn’t have any trouble getting himself ready to return to game action.

“I know the game,” Iverson said. “All the ins and outs of the game. So that won’t be a problem for me … 3-on-3 basketball, I played that all my life.”

But Sunday, the league’s most visible player off the court was largely invisible on it.

His team, 3’s Company, played in the third game, and the crowd went crazy when he was introduced last. But while he still has his trademark cornrows and headband, he very much looked like a 42-year-old trying to play hoops.

He struggled to get past anyone, missing his first four shots before finally draining a wide-open 15-footer early in the first half. That proved to be his only basket, and his only highlight.

Iverson — who said after the game he hadn’t been on a court in five years before being beginning to prepare to play in the league — spent the vast majority of the game in the coaching portion of his player/coach role. He bowed to the crowd’s wishes for him to return to the game in the first half when a full-throated “We Want A.I.!” chant broke out, but ignored it during the second half.

Later, he made it clear that fans planning to watch the league later this summer during its 10-city tour (including stops in Charlotte, Dallas, Philadelphia and Los Angeles) shouldn’t expect to see more than what he did Sunday.

“I signed up to be coach, player, [and] captain,” Iverson said after finishing with two points and two assists on 1-for-6 shooting. “The coach part is going to go on throughout the game. The playing part is not going to be what you expect. I’m 42 years old, been retired, what, six, seven years? The only reason I get out there for the couple minutes I do get out there is for the fans, you know what I mean?

“You’re not going to see the Allen Iverson of old out there.”

This, inherently, is the league’s problem. Fans arrived at Barclays Center Sunday hoping to see Iverson. And while the crowd remained surprisingly engaged throughout the day, most fans left after Iverson was done, and some booed play when he was on the sideline.

For as much as everyone associated with the league argued it was anything but a novelty act, fans didn’t pay to watch Iverson’s teammate, Andre Owens, finish with 20 points and 15 rebounds; they paid to watch Iverson. And if Iverson is only going to play token minutes, how long will the league be able to maintain interest?

Still, Sunday provided positives for the league’s organizers. The crowd was as large, and as good, as they could’ve hoped for. And there were a few moments of genuine excitement, including game-winning baskets to dramatically close out the first two games — an and-one layup by Rashard Lewis, and Stevenson’s three-pointer — that were met with standing ovations, and big celebrations by the victors.

“The sky’s the limit,” Iverson said, speaking of the league’s potential.

Only time will tell, however, if a league so reliant on nostalgia can become something sustainable, or if it is destined to be a novelty act that quickly loses its luster.