Russian gymnasts arrive before the qualifying for the men's artistic gymnastics competition in Rio de Janeiro on Saturday. (Thomas Coex/AFP/Getty Images)

Russian boxer Evgeny Tishchenko understood the booing he heard Monday afternoon as he strutted to the ring inside Riocentro Pavilion 6 and ducked under the ropes. He would face Brazilian Juan Nogueira, and naturally the raucous crowd would support a native son. What bothered Tischenko was how familiar the sound had already become.

The Russians, like characters from any garden-variety Cold War movie, are cast in the role of the villains at the Rio Olympics. During the first three days of competition, they have competed under the suspicion of fellow athletes and under the derision of otherwise neutral fans. More than 100 Russian athletes were banished from the Games because of their ties to a state-sanctioned doping program; the 270 or so who were cleared and are here to compete have encountered open hostility.

The accusations leveled by global anti-doping authorities on the eve of the Games about the extent of Russian cheating dating from 2011 ensured no athlete here can compete against a Russian without at least a healthy dose of uncertainty, and that no fans can watch a Russian perform without at least wondering if the results are legitimate.

After Tischenko beat Nogueira in a 91-kilogram (200-pound) preliminary bout, he expressed frustration at the persistent enmity toward his delegation.

“In general, it’s really a pity that the crowd performs this way of supporting [whoever is] against Russia,” Tishchenko said through a translator. “I’m really upset about it. It was the first time I faced such treatment. Actually, I’m a little bit disappointed about this.”

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His countryman Timur Safin could relate. During Sunday’s men’s foil bronze medal bout, Safin faced Britain’s Richard Kruse. The Carioca Arena 3 crowd, aside from a pocket of Russian fans, roared when Kruse scored a point and booed when Safin touched. When Safin won the bronze, Russia’s contingent drowned out the boos, but just barely.

“I did notice they were giving me a bit more support,” Kruse said Monday, chuckling. “I’d like to think they preferred my style of fencing.”

Of course, suspicions of cheating by athletes at Olympics did not begin with the Rio Games and with Russians. Athletes from a host of countries over the years, including several prominent Americans, have failed doping tests at the Olympics or competed under a cloud of doubt. But the extent of the Russian program, which purportedly was backed by some of the country’s senior leadership, and the timing of the World Anti-Doping Agency’s public acknowledgment of it 18 days before the Games opened have guaranteed that the focus here — at least for now — has been on the Russians.

Kruse said Britain’s fencers have discussed the details and implications of last month’s WADA report since arriving in Brazil. “We’ve been talking about virtually nothing else,” he said. The topics included guessing which Russian fencers most relied on strength and looked the most buff.

The discussion grew starker once Kruse lost a medal directly to a Russian. “I mean, look, I have absolutely no idea what’s going on,” Kruse said. “If this is a state-sponsored program of cheating, that’s obviously pretty sad for humanity. I’d like to see the best in people. Some of these Russians are very fit.”

Kruse levied no accusations and spoke in a cheerful, almost sympathetic tone. “If we assume all of them are doping, and they’re clean, then we’re disrespecting their life’s work,” Kruse said. But he also stated the reality that has turned Russians into rogues: It is difficult to trust the fairness of the Games.

“If the facts we’ve been given are true in the Western media, then yeah, of course it is,” Kruse said. “I just don’t know what to say. I hope they’re clean. I suppose the one positive result is, if it’s state-sponsored, I imagine the athletes wouldn’t have much choice. I imagine it’s you take it, or you’re down the salt mine. No one knows who’s clean and who’s not.”

Russian whistleblowers, first in a 2014 German television documentary and in New York Times and CBS “60 Minutes” reports this year, exposed a widespread, state-sponsored doping program that centered upon the 2014 Winter Olympics in Sochi, Russia. The reports prompted WADA to commission an investigation; the resulting report confirmed and detailed the Russians’ doping efforts.

The International Olympic Committee left the decision of whether and how to sanction Russian athletes who had not tested positive to individual sports federations. The probes and politics have left Russian athletes, clean or not, in awkward positions.

Most Russian athletes did not know if they would be permitted to compete until — or, in some cases, even after — the Games started. On Thursday, the IOC announced it had cleared 271 Russian athletes to compete. The number climbed after two Russian swimmers and a wrestler won appeals through the IOC’s Center of Arbitration for Sport. The center also rejected three cyclists hoping to overturn their exclusion, but some athletes questioned how they could be let back in.

“Clearly there’s more that needs to be done, and clearly the circumstances we’re dealing with is frustrating to a lot of athletes and unjust to a lot of athletes,” said U.S. swimmer Cody Miller, who won a bronze medal Sunday in the 100-meter breaststroke. “During this Games there will probably be people who miss the podium to people who don’t deserve to be on the podium. And that is wrong. And I don’t have a solution for that. But it’s wrong.”

The sense of Russian cheating is apparent at the swimming venue, where a host of Russian athletes — previously banned — have been allowed to compete because of a last-minute decision by FINA, the sport’s world governing body. Initially, FINA banned seven Russian swimmers. When some of those swimmers have appeared on the starting blocks, the reaction from the crowd at Olympic Aquatics Stadium has been unmistakable: boos.

The crowd booed Yulia Efimova, a 24-year-old breaststroker who was banned for 16 months for using anabolic steroids, later tested positive for the banned substance meldonium but had that ruling overturned. It booed the Russian men’s 4x100-meter freestyle relay team, which was introduced last before Sunday night’s final — won by the United States — because it had posted the top seed in that afternoon’s qualifying heats.

The reaction has been strongest among athletes and spectators; and it is the athletes who are speaking out, invoking the idea that politics are playing a role in determining who competes and who doesn’t.

“It’s like FINA keep going back on their word, and the IOC keep going back on their word,” Irish swimmer Fiona Doyle told reporters. “And FINA caved in to [Russian President Vladimir] Putin, and that’s just not fair on the rest of the athletes who are clean. Who are you supposed to trust now? They have signs all over the village saying we are a clean sport — and it’s not.”

Efimova was involved in perhaps the most visible spat between a previously banned Russian athlete and a competitor. When she won her semifinal in the 100-meter breaststroke Sunday night, she pointed her index finger in the air as an apparent reference to American Lilly King, who had gestured similarly after winning her afternoon heat.

As Efimova finished her race, NBC showed images of King watching on a monitor in the “ready room,” where swimmers wait before their events. Signaling her displeasure at Efimova’s gesture, King wagged her finger back-and-forth at the Russian.

“You know, you’re shaking your finger [to signal] number one and you’ve been caught for drug cheating,” King, standing poolside, explained to NBC afterward. “And I’m just not a fan.”

After King edged Efimova in Monday night’s final, she didn’t back off the rhetoric, saying, “It’s incredible — winning the gold medal and knowing I did it clean.”

Efimova, for her part, had nothing specific to say about the circumstances of her ban or her reinstatement. Following her heat Sunday afternoon, she declined further interview requests after stopping briefly to talk to wire service reporters.

“I don’t know what to do,” Effmova said. “It was crazy the last year-and-a-half. I didn’t understand what was going on. I’m just happy to be here and ready to race.”