The fan groups see each other as enemies instead of opponents.
The policie always has much work to do when there is a Sao Paulo against Palmeiras derby in the city of Sao Paulo. Regularly the fans from one team meet the fans from the other team in the subway and violence goes all the away.
The most violent fight between these fans happened in August 1995 after the final of an Under 20-Championship in Pacaembu Stadium. After Palmeiras scored the golden goal, some Palmeiras fans entered the pitch and stood in front of the São Paulo fans in order to tease them. The reaction of teh Sao Paulo fans was to charge the Palmeiras fans and started a big group fight against hundreds of Palmeiras fans. The police couldn't stop them and eventually a Sao Paulo fan died after being wildly hit on the head.