The joyful, communal festival of World Cup soccer that had seemingly brought the United States together has now been interrupted by a controversy that cuts through notions of fair play on and off the field.

And it was not hard to find opinions about it.

Last week, President Trump placed a phone call to the president of FIFA, world soccer’s governing body, that ultimately led to the reinstatement of a star U.S. player who had been suspended from Monday night’s game against Belgium in the round of 16. The player, Folarin Balogun, had been barred after getting a red card last week in a match against Bosnia and Herzegovina.

Reaction to the reversal ran from excitement to incredulity to strong condemnation.

“You can’t just call the president of FIFA and call for things to change,” Julie Foudy, a TV analyst and former stalwart on the U.S. women’s national team, said in a phone interview. “Soccer is a religion to people globally and when it doesn’t seem like it’s operated under any sense of fairness, you lose what’s so special about a World Cup.”

Some American fans agreed with the decision. Patrick McDonald, 48, who coaches high school soccer in Birmingham, Ala., pointed to his own league, where he says controversial calls have been reviewed and later reversed.

“I know an injustice was corrected and it benefited my team and I’m happy with it,” he said.

Others were excited to see Balogun play — he has scored three goals in this World Cup — but they had misgivings about Mr. Trump’s influence.

“I was shocked,” said Ethan Engelken, 23, from Milwaukee, as he was getting coffee at Pike Place Market in Seattle on Monday morning. “Excited but shocked. And confused.”

He could see how a U.S. victory on Monday night might appear tainted now. “I’d probably celebrate it like it never happened,” Mr. Engelken said. “But I can see that argument.”

John Reed, 35, a youth pastor in an Atlanta suburb, said that since the United States was benefiting from the interference, “I’m not too upset by it.”

“FIFA is so freaking corrupt anyway,” he said. “But we shouldn’t have politicians interfering.”

Indeed, FIFA’s history is littered with corruption cases. In recent years, that has included the opaque bidding process that put the 2022 World Cup in Qatar and a $150 million bribery scheme that forced the ouster of Sepp Blatter as FIFA president.

When Charnita West Jenkins, from Stonecrest, Ga., learned about the call, she looked at a replay of the game.

The red card was a bad call, she said. But she believed it should stand.

“Why is the president involved in a soccer match?” said Ms. West Jenkins, who has been a soccer fan since spending the summer in England during the 2006 World Cup. “Once you change the rules you taint the game.”

Beyond the game, Ms. West Jenkins, 55, also objected to the politics around Mr. Trump’s call. In her eyes, his intervention also highlighted what she described as his convenient stance on birthright citizenship.

“The president is talking out both sides of his mouth,” she said.

Balogun is eligible to play for the United States only because his mother was stopped by airline employees from flying home to London when she was seven months pregnant. She gave birth to him in New York before returning home, making her son a U.S. citizen.

It was just last week that Mr. Trump lost a case before the Supreme Court that would have deprived birthright citizenship to people like Balogun.

“Trump is going to bat for a player who if it were up to him wouldn’t be playing for the U.S. national team,” said Jeff Wolfe, a season-ticket holder for Los Angeles FC of Major League Soccer who attended the game against Bosnia and Herzegovina. “But do you ever expect Trump to be conscientious, thoughtful and considerate? I feel badly for the U.S. players and for Balogun — the way he handled it afterward was amazing.”

Others criticized FIFA.

“It shows favoritism toward the U.S.A.,” said Matt Gilley, a 41-year-old lobsterman from Maine. If FIFA “thought the call was wrong, they should have reversed the call, not kicked the can down the road a year.”

Balogun was given a red card after coming down hard on a Bosnian player’s ankle in a match last Wednesday. A red card had meant an automatic suspension for the next match.

But hours later, Mr. Trump called Gianni Infantino, FIFA’s current president, and on Sunday the organization reversed itself, saying that Mr. Balogun could play against Belgium.

On Monday, Mr. Trump defended his actions but denied telling Mr. Infantino what to do. “I don’t believe he made the decision. I think it was a committee that made the decision. And they made the right decision,” he said.

Mr. Infantino has made extensive efforts to win Mr. Trump’s favor. Last year, he gave Mr. Trump a “FIFA Peace Prize” after the president’s unsuccessful campaign to win the Nobel Peace Prize. FIFA had never awarded such a prize.

Eric Miller, of Snohomish, Wash., said he hoped Mr. Trump did not act inappropriately to get Balogun’s red card suspended, and said he was not surprised politicians would ask for a review any time there’s a controversial call.

A Navy veteran, Mr. Miller, 32, was wearing a hat with a stuffed eagle on top of it on his light rail ride to the stadium on Monday after picking up last-minute tickets to go with his wife and a co-worker.

He said he hoped the geopolitical storm wouldn’t overshadow the game, and that other countries like England — which had a red card on Sunday — also challenge their infractions to help combat the notion that a host country had been favored.

“I’m not against it as long as it’s not threatening or intimidation or using the government against them,” Mr. Miller said.

Stephanie Brock, 50, who runs a commercial interior design firm in Portland, Maine, said Mr. Trump’s intervention and the resulting reversal was “a bad look for the sport.”

“The fix is more corrosive than the original questionable call,” she said.

Reporting was contributed by Tim Arango, Eduardo Medina, Audra D. S. Burch, Jenna Russell and Sally Ho.