Thousands of people took part in marches in Vienna against the annual ball that was expected to be attended by foreign far-right leaders.
The protesters were opposed to Austria's opposition Freedom Party (FPÖ) holding its Akademikerball in the city's imperial Hofburg palace.
Several people were arrested after outbreaks of violence.
Josef S is accused of inciting 500 anti-fascist protesters to attack police and damage a police car. If convicted of serious and deliberate injury he faces up to five years in prison.
The total damage from the protests amounted to €500,000 euros.
An internet campaign called Free Josef is calling for people to support the student and contribute to his legal fees.
The start of the trial was surprisingly quiet, reported Der Kurier paper. Fifty people attended the court hearing and 30 people gathered outside. Josef S, wearing glasses and a jacket and tie, looked more like a preppy high school student than the violent leader of a left-wing group.
"We raised him with love and care, and it's really bad, the picture that is being drawn of him," Josef’s father said, shortly before the trial began.
His mother, who visited him in prison two weeks ago, said she cannot believe that her son is guilty, as he has never done anything similar before. His parents are hoping for an acquittal.
The prosecutor said at the start of the trial that all the protesters who had travelled from Germany, had only one goal, and that was violence. He also spoke of "images like a war zone" in the aftermath of the protests.
Josef has pleaded not guilty. He said that he had had no intention of attacking police officers, and even though he was caught on video with a rubbish bin in his hand, he never intended to throw it at the police. He has already spent four and a half months in prison.
The main witness is a police official who saw Josef featured in a television report, and identified him as one of the ringleaders.
The Akademikerball replaced the controversial WKR Ball which ran as part of Vienna's annual ball season until two years ago. It was traditionally organised by student fraternities, which include far-right members from across Europe.