MOSCOW -- Yaroslav G. Belousov, a political science student, found himself in the center of the mayhem last year when a rally against Vladimir V. Putin, then the prime minister, unexpectedly turned violent. As protesters grappled with riot police officers in helmets swinging truncheons, investigators say, Mr. Belousov "threw rocks and pieces of asphalt, broke through the cordon and attacked police officers."
Some of his supporters, citing video evidence, say he threw only a lemon.
Mr. Belousov, 21 and the father of a 2-year-old son, had no previous criminal record, but he has been in jail for a year and could serve 12 more years if convicted on all counts. He is one of a dozen participants in the May 6, 2012, demonstration -- representing a cross section of the middle-class Muscovites who turned decisively against Mr. Putin -- whose trial opened Thursday in a Moscow court. Legal experts say they face stiff sentences and slim chances of acquittal.
What sets the case apart from a series of recent political prosecutions in Russia is that not one of the defendants was a high-profile opposition leader when arrested. Most are unknown to the public, and their prosecution seems intended as a sharp warning to other ordinary Russians, especially educated professionals, about taking part in street protests.
"When they arrest not the leaders, not the heads of the opposition but the ordinary people representing different social strata, of different ages and views, when these people are just being pulled out, this is, of course, intimidation," Tamara Belousova, Mr. Belousov's wife, said Wednesday in an interview at a cafe across the street from Red Square.
The case against Mr. Belousov and his co-defendants, along with a barrage of criminal cases against opposition leaders, has succeeded in suppressing the protest movement, as its initial enthusiasm has been overtaken by fear and exhaustion.
But Ms. Belousova, 21, also a political science student, predicted that ultimately the government's strategy would backfire. "Because it causes indignation," she said, adding: "Our child is 2 years old, and he hasn't seen his father for a whole year. The cruelty is absolute and unjustified."
Mr. Belousov, like his wife, was working toward a degree at Moscow State University, and attended the protest on Bolotnaya Square, she said, largely because of his research interest in social media as a tool of political organizing.
Five of the defendants now on trial were students; six were self-declared political activists of varying views. Their ranks include a freelance journalist, a sales manager, an artist and a subway worker. Several were not previously active in politics.
They range in age from 19 to 51, but most are in their 20s, and among them are liberals, leftists and an anarchist. The 10 men in the group have all been detained for about a year, while the two women were released, one on her own recognizance and the other under house arrest.
More famous Russians say they also are afraid of losing their freedom. Garry Kasparov, the chess champion and longtime opposition figure, said at a news conference in Geneva last week that he would not return to Russia for fear of arrest related to his participation in the protests.
On Facebook, he wrote, "Putin is cracking down harder than ever and is showing he is willing to create a new generation of political prisoners unseen since the days of Stalin."
In the trial that opened Thursday, the only defendant with name recognition, Maria Baronova, was a former press aide to an opposition lawmaker, Ilya V. Ponomarev, and gained prominence only after her arrest. Released on her own recognizance, she faces the lightest charges, of inciting disobedience and mass riots. Most defendants are charged with participating in riots and assaulting police officers.
Dmitry V. Agranovsky, a lawyer who is representing Mr. Belousov and a second defendant, Vladimir Akimenkov, said in a telephone interview that the lengthy pretrial detention of most of the defendants was proof of the political nature of the charges.
"It's not normal or regular that these people have been held for about a year," Mr. Agranovsky said. "They don't hold them that long, especially when they don't have any priors. But if the case touches on politics, and if there are opposition members among those arrested, then it's normal practice to be harsher toward them."
The big street protests in Moscow, which began after disputed parliamentary elections in December 2011, were overwhelmingly peaceful until May 6, the day before Mr. Putin's inauguration for a third term as president. At that point, the demonstrations had lost momentum, and the crowd, estimated at 20,000 people, was a fraction of the size of previous events.
Among the participants were parents with children and older people, with no expectation of violence. But at some point a fracas broke out where police barricades created a bottleneck for the crowds entering the square.
Mr. Agranovsky said the charges against Mr. Belousov were based heavily on the dubious testimony of a single police officer who claimed to be injured during the melee.
"I don't think that he was hurt really," he said. "The injured police officer said that Belousov threw a small yellow object at his chest. A riot police officer's chest is protected by a serious guard, some sort of Kevlar vest, which can withstand at the very least knives, and maybe things stronger."
Mr. Agranovsky said the evidence against his second client, Mr. Akimenkov, an activist with the Left Front, a socialist group, was even thinner: testimony from a police officer whose recollection of the clash has changed several times.
Farit T. Murtazin, the lawyer for Artyom Savyolov, 36, a construction worker employed by the Moscow subway, said his client had lived with his aging father, whom he cared for, before being arrested at the rally.
Mr. Murtazin said it was Mr. Savyolov's first political protest. "He came because this rally was authorized," he said, adding: "He was not happy with the results of the election. This is his right." The authorities initially accused Mr. Savyolov of shouting antigovernment slogans, he said, but dropped that after learning he had a lifelong stutter.
The federal Investigative Committee, which led the inquiry, has said it has video evidence of the crimes, and the authorities have said violence against the police will not be tolerated.
Zoya Svetova, a journalist at The New Times magazine and a member of the Public Oversight Committee, which monitors prison conditions, said the defendants had gained new self-awareness. "Already they are not just some people who randomly went out to protest on a square," said Ms. Svetova, who has visited several of them in jail. "They realize that they are political prisoners, activists who are facing repression."
Ms. Belousova described her husband as a scholarly man interested in political science but not politically active or an oppositionist. She said he had poor eyesight and asthma, which she said was being exacerbated by his cellmates' smoking. And she said he desperately missed his son.
"He is a man of books," she said. "And this saves him now that he is in jail." She added, "I asked him how he celebrated the New Year; he answered that he finished reading five volumes of the history of the Middle Ages."
But Mr. Belousov's lawyer said he was not optimistic about the trial. "Maybe they'll reduce the sentence," he said. "In Russia there are practically no acquittals."
This article originally appeared in The New York Times.