In another episode of unruly fan behavior during the NBA playoffs, a water bottle thrown Sunday from the stands at Boston’s TD Garden flew near the head of Kyrie Irving as the Brooklyn Nets star was leaving the court following a Game 4 defeat of the host Celtics.

“It’s unfortunate that sports has come to this kind of crossroads, where you’re seeing a lot of old ways come up,” Irving said after the Nets’ 141-126 win gave them a 3-1 lead in their first-round, best-of-seven playoff series with the Celtics.

“Just underlying racism, and treating people like they’re in a human zoo. You know, throwing stuff at people and saying things. There’s a certain point where it just gets to be too much.”

Irving, 29, referred to the “subtle racism” he had talked about hoping to avoid from Boston fans before the series shifted from Brooklyn to TD Garden for Games 3 and 4. After scoring 39 points and grabbing 11 rebounds on Sunday, the former Celtics player claimed that he had “called things out before they happened” with those comments.

A replay of the sequence on TNT’s postgame coverage appeared to show a fan in a Celtics jersey, bearing the name and number of former Boston star Kevin Garnett, throwing the bottle. That fan was then shown being handcuffed and led by police out of the arena. According to reports, he was subsequently arrested and banned for life from TD Garden.

Irving was also shown appearing to make a point of stepping on the Celtics’ logo at midcourt as he and Nets teammates congratulated each other for the win. During a two-season stint with the Celtics between 2017 and 2019, he angered some Celtics fans for what they saw as poor leadership even before he reneged on a pledge to re-sign with the team.

During Friday’s Game 3, a Boston win, and Game 4, Irving was loudly booed by fans at TD Garden.

“We know how these people are here in Boston, and we know how passionate they are about Kyrie, in particular,” the Nets’ Kevin Durant, who had 42 points Sunday, said after the game. “They’re still upset at him. That’s no reason for them to act childish.”

“Glad we got the [win],” Durant added, “and hopefully we don’t have to come back here this year.”

Brooklyn can close out the series with a victory Tuesday in Brooklyn. The NBA, meanwhile, has another ugly episode on its hands.

Earlier in the playoffs, during which the NBA has welcomed varying amounts of fans after staging last year’s postseason and much of this season without them amid the coronavirus pandemic, the 76ers banned a fan from Philadelphia’s Wells Fargo Center after the Washington Wizards’ Russell Westbrook had popcorn dumped on him. The New York Knicks banned a fan from Madison Square Garden after a video appeared to show him spitting in the direction of the Atlanta Hawks’ Trae Young, and the Utah Jazz banned three fans for what the team and players said were racist and vulgar comments toward the parents of the Memphis Grizzlies’ Ja Morant.

The NBA issued a statement Thursday in which it said that the return of crowds to arenas has “brought great excitement and energy to the start of the playoffs, but it is critical that we all show respect for our players, officials and our fellow fans.” The league added that an “enhanced” code of conduct or fans will be “vigorously enforced in order to ensure a safe and respectful environment for all involved.”

“I know that being in a house for a year and a half with the pandemic has got a lot of people on edge, got a lot of people stressed out,” Durant said Sunday. “But when you come to these games, you’ve got to realize, these men are human. We’re not animals, we’re not in a circus. You coming to the game is not all about you as a fan.

“So have some respect for the game, have some respect for these human beings, and have some respect for yourself. Your mother wouldn’t be proud of you throwing water bottles at basketball players, or spitting on players or tossing popcorn.

“So grow the [expletive] up and enjoy the game,” Durant continued. “It’s bigger than you.”

Calling the bottle-throwing and other incidents “really unacceptable,” Brooklyn’s James Harden said that “somebody has to be made an example.”

“I don’t think just banning fans from the arena is good enough,” said Harden, who had 23 points and 18 assists in the Game 4 win, “because at different arenas you continue to see fans doing it, so something has to be put in place.”

Celtics guard Marcus Smart, who said before Game 3 that, as with Irving, he had heard Boston fans make racist comments, asserted Sunday that the actions of one fan should not tarnish the group.

“We just had a knucklehead do something knucklehead-ish,” said Smart, who is in his seventh season in Boston.

TNT analyst Charles Barkley, a Hall of Fame former player, said of the fan who allegedly threw the water bottle, “Just take him downstairs and let Kyrie handle that.”

In his comments last week, Irving had said: “I’m just looking forward to competing with my teammates, and hopefully we can just keep it strictly basketball, there’s no belligerence or any racism going on, subtle racism and people yelling [stuff] from the crowd. But even if it is, it’s part of the nature of the game and we’re just going to focus on what we can control.”

After he, Durant and Harden combined for 104 points Sunday — tied for the most by a trio from one team in NBA playoff history — Irving told reporters, “We keep saying, ‘We’re human, we’re human,’ but we don’t get treated like we have rights when we’re out there at times.”

“I called it out,” he added. “I just wanted it to be strictly basketball, and then you can see that people just feel very entitled out here.”

“It’s a reflection on us as a whole,” Irving said, “when you have fans acting like that.”