This week's worst disturbances paralyzed parts of Sao Paolo, where damage from marauding marchers' random attacks on urban property was said to be extensive, multiple media reports said.
Officials blame an anarchist group called Black Bloc but critics say the official contention doesn't add up to the full story behind the latest violence, which is rooted in public discontent over many issues.
Police used teargas to control the protesters and made at least 92 arrests.
A million people went on the march in June to heap indignation on President Dilma Rousseff's administration, faulting her for a whole range of alleged failures -- from an ineffective crackdown on corruption in public institutions, to unbridled crime in Brazil's cities, to unnecessarily high spending on Brazil's preparations for FIFA World Cup next year and the Summer Olympics in 2016.
Her critics in the opposition and influential media say the government spending on those two prestige projects could be more justifiable if the government would enforce greater checks and balances, fight graft, inefficiencies, cronyism and neglect of the country's more pressing poverty reduction and infrastructure programs.
Millions of Brazilians live in squalor next to neighborhoods marked out by critics for consumer excess, affluence and comforts enjoyed by a small minority of wealthy or middle class citizens.
Crime infestation of favela slums and high homicide rates have angered Brazilians who see those problems as a shameful blight for a nation masquerading, critics say, behind an entirely different exterior presentation to the world outside.
Police reported at least 90 arrests in the latest riots after protesters torched public transport buses and other vehicles. The police killing of 17-year-old Douglas Rodrigues triggered the riots, news media reported.
Some protesters carried firearms and one person was taken to hospital with gunshot wounds, police said.
There have been scant eyewitness reports, an indication that the news media are effectively intimidated by the unpredictable nature of police and security forces' response. Journalists routinely complain of harassment by law enforcement agents.
Police say an officer responding to a disturbance in the city's northern Vila Medeiros neighborhood accidentally shot Rodrigues, who was rushed to hospital and died there.
As the news of the boy's death spread, hundreds of angry youths went on a rampage, attacking banks, cash dispensing machines, shops and vehicles.
Sao Paulo has a sprawling metropolitan area with 20 million inhabitants and sharp differences in quality of housing and life across neighborhoods. It is the city chosen to host the opening game of the World Cup June 12, 2014.
Government ministers have taken pains to reassure FIFA officials, other international organizations and tourism operators that unrest during the tournaments is very unlikely. Brazilians will be more interested in celebrating the games than complaining about their cost, Sports Minister Aldo Rebelo said.