RIO DE JANEIRO (Reuters) - Olympic athletes and visitors might be forgiven if they feel like they accidentally stepped into one of Brazil's notoriously raucous football arenas, where insults, boos and outright hostility toward rival teams are common.
Be it at boxing, judo, fencing, or even tennis, hometown Brazil fans are treating many Olympic sports as if they were at Flamengo vs. Fluminense, a crosstown Rio rivalry where passions, in addition to spit and occasionally fists, frequently fly.
Early on Sunday, as Brazilian fencer Ghislain Perrier, parried lunges by Ma Jianfei, the local crowd jeered the Chinese rival, even though he won. At Rio tennis, a far cry from the practiced seriousness of tournaments like Wimbledon, Brazilian fans mocked Germany's Dustin Brown, ranked 86 in the world, when he missed an easy shot.
''Brazilian fans have no manners,'' says Juca Kfouri, a prominent Brazilian sportswriter and commentator. ''You will not find any respect for rivals or any of the Olympic spirit you might have had in London.''
Brazil's sporting culture, largely defined by the country's past success in football, is dominated by an often jingoistic attitude toward anyone not donning the local yellow.
''People seem to think it's a football match,'' says Guilherme Toldo, a Brazilian fencer who on Sunday was surprised by local booing, air horns and stomping directed at foreign rivals in what is traditionally a more somber sport.
At an event like the Olympics, where ticketholders hail mostly from an upper-middle and wealthy class that is used to being pampered, the chest-thumping can be especially jarring, even to many local fans.
''That was not elegant,'' said Thiago Pereira, a Brazilian who cringed as some compatriots booed when arch-rival Argentina's athletes paraded during the opening ceremony on Friday.
So rude can Brazil fans be that two years ago, at the inaugural game of the football World Cup in São Paulo, a largely upper-class crowd chanted for Dilma Rousseff, Brazil's first female president and one of many dignitaries in attendance, to ''go to take it in the (expletive).''
Athletes say the hostility can affect results.
''I am very disappointed,'' said Hassan N'Dam N'jikam, a Cameroonian fighter who was loudly booed and lost to a local on Saturday even though most boxing writers and foreigners in the audience thought he outpunched his Brazilian opponent.
The noise, he said, ''plays into the judgment.''
For Brazilian athletes, or course, the climate can help.
''When you play in Europe, the people are more calm,'' said Thomaz Bellucci, the Brazilian tennis player who progressed after Brown, the German, twisted an ankle in their match. ''In Brazil, people go crazy and it's very nice.''
Sometimes, Brazil fans are protesting perceived slights.
American women's goalkeeper Hope Solo, for instance, was jeered by Brazilians after she joked about the Zika virus, which caused serious health issues in Brazil before it spread to other countries, including the United States.
A boxer from Australia, whose delegation refused to move into Olympic housing before the Games because of plumbing and electrical flaws in their rooms, was taunted on Saturday before he even entered the ring -- against a Brazilian opponent, no less.
The Brazilian, heavyweight Juan Nogueira, won.
Additional reporting by Rodrigo Viga Gaier, Pedro Fonseca, Brad Haynes and Nick Mulvenney; editing by Neil Robinson.