When the Australian equestrian and three-time Olympic medalist Shane Rose mounted his horse for a costumed competition wearing only a G-string bikini, or “mankini,” he thought it was all in good — albeit somewhat uncomfortable — fun.

Mr. Rose, 50, wasn’t expecting to receive a call from Australia’s governing equestrian body notifying him that he was under investigation and temporarily barred from competing. But he did, and for a few days after the competition on Feb. 11, he feared that the episode might derail his preparations for the Paris Olympics.

On Monday, the body, Equestrian Australia, said it had cleared Mr. Rose of wrongdoing at the event. But in a country of unselfconscious beachgoers, where small, tight swimwear is a common sight even on prime ministers, the incident had already made national headlines and sparked a barrage of jokes and criticism of the investigation on social media. A few supporters even wore mankinis of their own in solidarity.

Matt Shirvington, a news presenter on Seven Network and a former Olympic runner, jokingly threatened in a television broadcast on Monday morning that if Mr. Rose wasn’t able to attend the Olympics because of his mankini, current and former Olympians would start wearing them too.

“We’ve got to take a stand here,” he said.

Mr. Rose, a horse trainer and equestrian from the town of Werombi in New South Wales, specializes in eventing, an equestrian sport that includes dressage, cross-country and show jumping. He won silver medals in the 2008 and 2020 Olympics, and bronze in 2016.

Last weekend, he rode in the Wallaby Hill Extravaganza, a competition in the town of Robertson with a dress-up component. He wore three costumes: a gorilla suit, a Duffman beer costume from the Simpsons and a mankini, an outfit popularized by the 2006 movie “Borat.”

“It’s a dress-up competition, and I thought it’d be funny to go in a mankini,” he said in an interview. “That’s what I was intending — just to have a laugh.”

He rode for about 10 minutes in the costume — “a short a period as I could make it” — and said that it was not an experience he was eager to repeat.

“I’ve never worn a G-string before, and I can’t recommend it to anyone,” he said.

A few days after the competition, he said, Equestrian Australia told him it had received a complaint about his costumes and planned to investigate. The group later said as much publicly, noting that Mr. Rose was bound by the body’s code of conduct.

Last Friday, the group told him that he could not compete until the investigation ended, Mr. Rose said. It was unclear what specific part of Equestrian Australia’s code of conduct Mr. Rose had breached.

The punishment for violating the code of conduct could have ranged from a warning to a suspension, according to Equestrian Australia’s disciplinary policy.

Mr. Rose posted, and then deleted, an apology to Facebook. Equestrian Australia’s statement on Monday said that its finding had taken the apology, and the fact that the event in question was not a professional competition.

The investigation struck some as particularly strange because tight, revealing swimwear is common on Australian beaches. “Budgie smugglers” — small, stretchy swimming briefs that make it appear as though the wearer is trying to conceal a budgerigar, or small parrot — have been worn by so many prime ministers that one newspaper described them as “part of the unofficial political uniform.”

As news of Mr. Rose’s mankini rippled across the country over the weekend, many Australians expressed support for him.

Bowral Kubota, a supplier of construction and farm machinery that sponsors the Wallaby Hill Extravaganza, pledged that it would give all attendees at next year’s event free mankinis “to embrace Shane’s sense of humor.”

Matt Williams, another Australian equestrian who has competed in three Olympic Games, said on Facebook: “Shane’s mankini was a great example of someone willing to do what it takes to entertain and strum up publicity in what is otherwise a very boring industry to the outside world.”

When the Australian equestrian and three-time Olympic medalist Shane Rose mounted his horse for a costumed competition wearing only a G-string bikini, or “mankini,” he thought it was all in good — albeit somewhat uncomfortable — fun.

Mr. Rose, 50, wasn’t expecting to receive a call from Australia’s governing equestrian body notifying him that he was under investigation and temporarily barred from competing. But he did, and for a few days after the competition on Feb. 11, he feared that the episode might derail his preparations for the Paris Olympics.

On Monday, the body, Equestrian Australia, said it had cleared Mr. Rose of wrongdoing at the event. But in a country of unselfconscious beachgoers, where small, tight swimwear is a common sight even on prime ministers, the incident had already made national headlines and sparked a barrage of jokes and criticism of the investigation on social media. A few supporters even wore mankinis of their own in solidarity.

Matt Shirvington, a news presenter on Seven Network and a former Olympic runner, jokingly threatened in a television broadcast on Monday morning that if Mr. Rose wasn’t able to attend the Olympics because of his mankini, current and former Olympians would start wearing them too.

“We’ve got to take a stand here,” he said.

Mr. Rose, a horse trainer and equestrian from the town of Werombi in New South Wales, specializes in eventing, an equestrian sport that includes dressage, cross-country and show jumping. He won silver medals in the 2008 and 2020 Olympics, and bronze in 2016.

Last weekend, he rode in the Wallaby Hill Extravaganza, a competition in the town of Robertson with a dress-up component. He wore three costumes: a gorilla suit, a Duffman beer costume from the Simpsons and a mankini, an outfit popularized by the 2006 movie “Borat.”

“It’s a dress-up competition, and I thought it’d be funny to go in a mankini,” he said in an interview. “That’s what I was intending — just to have a laugh.”

He rode for about 10 minutes in the costume — “a short a period as I could make it” — and said that it was not an experience he was eager to repeat.

“I’ve never worn a G-string before, and I can’t recommend it to anyone,” he said.

A few days after the competition, he said, Equestrian Australia told him it had received a complaint about his costumes and planned to investigate. The group later said as much publicly, noting that Mr. Rose was bound by the body’s code of conduct.

Last Friday, the group told him that he could not compete until the investigation ended, Mr. Rose said. It was unclear what specific part of Equestrian Australia’s code of conduct Mr. Rose had breached.

The punishment for violating the code of conduct could have ranged from a warning to a suspension, according to Equestrian Australia’s disciplinary policy.

Mr. Rose posted, and then deleted, an apology to Facebook. Equestrian Australia’s statement on Monday said that its finding had taken the apology, and the fact that the event in question was not a professional competition.

The investigation struck some as particularly strange because tight, revealing swimwear is common on Australian beaches. “Budgie smugglers” — small, stretchy swimming briefs that make it appear as though the wearer is trying to conceal a budgerigar, or small parrot — have been worn by so many prime ministers that one newspaper described them as “part of the unofficial political uniform.”

As news of Mr. Rose’s mankini rippled across the country over the weekend, many Australians expressed support for him.

Bowral Kubota, a supplier of construction and farm machinery that sponsors the Wallaby Hill Extravaganza, pledged that it would give all attendees at next year’s event free mankinis “to embrace Shane’s sense of humor.”

Matt Williams, another Australian equestrian who has competed in three Olympic Games, said on Facebook: “Shane’s mankini was a great example of someone willing to do what it takes to entertain and strum up publicity in what is otherwise a very boring industry to the outside world.”