In this account "Black Bloc" is presented as one side, and the police as another. They are the same side. Black Bloc is undercover police.
Police stand around and a journalist dies while covering a protest in Brazil | Public Radio International: "This particular protest was part of an on-going protest over public transportation fares. It’s part of the so-called “Free Pass” movement. And it took place at the central train station. Davies says a group of protesters called the “Black Blocs” were destroying ticketing machines.
But Davies says both sides are to blame.
He says the police are military police and do little to contain the protests. In this instance, the police just fired tear gas and stun grenades into the area as hundreds of commuters were heading home from work at around 7pm in the evening."