NEW YORK (AP) — Alexander Zverev felt he had to react when he heard a fan use language from Adolf Hitler's Nazi regime during his U.S. Open match.

This wasn't the type of heckling that players are prepared to face and trained to ignore. This man was sitting in a crowded section close to the court, where many more people besides the 2020 runner-up could hear the offensive words. So Zverev complained to the chair umpire and the man was ejected.

“At the end of the day I said what I said, the umpire immediately said, ‘OK, we’re going to get him out,’ and that’s it,” Zverev said.

It highlighted a challenge faced by players and the U.S. Open itself as the event draws the biggest crowds in its history: making sure fans are engaged but not disrupting the tennis — and how to respond when they do.

Another fan was thrown out Tuesday when he screamed at a key moment during Novak Djokovic's quarterfinal victory over Taylor Fritz, distracting the 23-time Grand Slam champion enough to cost him that point and then having screams directed back at him when Djokovic lost the next point, too.

“Look, it happens,” Djokovic said. “Sometimes you react, but most of the time you don’t. I speak for myself. Obviously there is, whatever percent of the time, you don’t react. People speak, they move around. You’ve got to be ready for that, particularly in the U.S. Open, especially in the night sessions.”

More than 500,000 fans attended the first week of the tournament, over 200,000 alone during the three-day Labor Day weekend. They were made aware of the code of conduct, which threatens expulsion or even arrest for, among other things, using abusive or threatening language, or behavior that creates a disruptive atmosphere or detrimental experience for players.

That made the ejection of the Zverev fan — who was not arrested — an easy decision. Same with throwing out two men last year when one was giving the other a haircut in the Arthur Ashe Stadium seats.

Less clear is a situation like the Djokovic fan, whose behavior is normal at a basketball or football game, where spectators don't hold their applause until play has stopped.

“If somebody is cheering loud, it’s different from somebody being abusive,” said Victoria Azarenka, a three-time U.S. Open finalist. “I think that as long as there is no abuse, I think that cheering loud is something that’s part of the sport.”

Chair umpires frequently urge fans to be courteous to players, or ask for quiet. But with some patrons heading directly to one of the drinking establishments on site well before heading to their seats, good luck getting all of them to cooperate.

“Everyone past 3 p.m. is drunk as hell, just having an unbelievable time,” Frances Tiafoe, a 2022 semifinalist, said before the tournament. “The ref has no shot at controlling that atmosphere.”

It's clearly bothering some players.

Daniil Medvedev was aggravated by some cheering between his first and second serves, saying it was grounds for the fans' removal. Laura Siegemund was in tears after her first-round loss to Coco Gauff, upset at what she felt was overly harsh treatment by the fans.

Medvedev, the 2021 U.S. Open champion, said outbursts between serves are not just a nuisance. He said some players bounce the ball 10 or more times before they serve, giving them time to refocus if a fan shouts. But he takes only two or three and wants to hit quickly, and believes rules protect him from someone trying to prevent it.

“Again, if the rule one day is going to change, I’m not going to argue against this anymore, because that’s the rule,” Medvedev said. “For the moment, the rule on the tennis court (is) you cannot do it. If the guy does it two times, I’m like, throw him out. He cannot do it. It’s the rule.”

Tiafoe advocates tennis encouraging fans to cheer and move around freely, like team sports. Others stress the need to hear while playing to gauge the speed of the ball coming at them, with Azarenka recalling a match in Miami when she couldn't.

“It was the music that was coming from the bar and it felt like South Beach,” she said. “It was absolutely unacceptable because I couldn’t hear the ball bounce at all.”

Still, Azarenka said she wouldn't ask for non-abusive fans' removal just for being loud. Same with Djokovic, who wants fans to feel part of the action.

“At the end of the day, they pay tickets to come and watch you play, so we try to put on a show and perform for them so they go back home satisfied that they have been here and enjoyed their day,” Djokovic said.

“But in those important moments when you’re all of a sudden under a lot of stress and you’re facing a break point and then all of a sudden everything annoys you and distracts you,” he added, “then you react.”

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AP tennis: https://apnews.com/hub/tennis