FIFA and the Brazilian government have said that violence at a Brazilian championship match is not an indication of what can be expected when the country hosts next year's World Cup.
Three people were seriously injured when fans fought running battles at a match between Atletico Paranaense and Vasco da Gama yesterday.

It is another blow for World Cup organisers, with at least 30 people killed in incidents in and around Brazil's stadiums this year.
Yesterday's game, on the final day of the season, had to be halted for 70 minutes as rival fans chased each other around the terraces, trading blows with home-made clubs and weapons.
Brazil's Sports Ministry condemned the violence and called for swift punishment for hooligans.

It also said it would consult with public prosecutors and police chiefs over security at matches. There were no police inside the Arena Joinville where the game took place because the home side had opted to use private security guards.

Brazilian President Dilma Rousseff also condemned the troublemakers and called for a special police station to be set up to deal with football-related incidents.
"I can assure you the lamentable scenes we saw yesterday will not be seen at the World Cup," said Andrei Rodrigues, the special secretary of major events at the Justice Ministry.
"We can assure you that the stadiums at the World Cup will have at least 200 camera feeds providing real time video and what happened yesterday cannot happen at the World Cup."

FIFA has also moved to tell fans that they should not fear violence at next year's tournament, which is to be held in 12 new or totally modernised stadiums across the country.
Unlike games in the national championship, which are organised by local clubs under the auspices of the Brazilian Football Confederation, World Cup matches are organised by FIFA and will count on heavy security both inside and outside the stadiums.

In addition, only 8% of tickets for each match go directly to the fans of the teams involved.
"For the 2014 FIFA World Cup a very comprehensive security concept is in place in an integrated operation between private and public security authorities to ensure the safety for fans, players and any other stakeholder involved in the event," FIFA said in a statement.

"The concept has worked very well during the FIFA Confederations Cup [in Brazil this year] and is built on models used at previous FIFA World Cups."

I was watching that match too. Military helicopters had to be called in.

EDIT: I also remember when there was a shootout at a Santos Laguna game.