This is something that should not happen in soccer mainly because soccer is for entertainment. I believe that fights like these are what makes families with small children not go to the stadium to see the game. Brazil should be an example since it will be hosting the 2014 world cup.
There was another strange fight between two gangs: Força Jovem Vasco and Torcida Fúria Independente. Vasco's fans stole a flag from the the rival gang and the police had to hit the fans to try to get the flag back. 52 thousand tickets were sold before the match, and the game ended Vasco 1 x 0 Guarani at Maracanã.