I don’t get it either. Isn’t green and yellow the Brazil colors? So you’re telling me if the national team wanted to play a game there, they would tell them to F off?
Naw, club-team rivalries. Green is the main color associated with
Palmeiras, the arch-rival of
Corinthians, the team whose stadium hosted the first (and, I hope, last) NFL game in Brazil.
Gaviões da Fiel and Mancha Verde are samba schools that compete in the top division in São Paulo on the weekend of Carnava.l Those samba schools had their origins in organized groups of fans of Corinthians and Palmeiras, respectively.
Fans of teams in Brazil have organized groups who cheer (and drum and sing) for the team together before, during, and after games. The first one to have defined and recorded internal rules was Gaviões da Fiel. As an organized group, Gaviões had certain tactical advantages in brawls with opposing teams' fans. Palmeiras fans formed Mancha Verde at least in part as a defense against Gaviões.
There have been huge brawls between those fan groups, but by the aughts, the organized fan groups had gotten a lot of political power with their respective teams and near the main organized groups at games became the safest places in the stadium because the organized groups did not tolerate any bull$#!+ because the leaders knew the police were always watching them.
Gaviões and Mancha are still very present in the in-stadium audience for their respective teams' games, but they are no longer in gang-style war. Their samba schools compete against each other. Technically, the fan organization Mancha Verde hasn't existed since 1995, but all the members just joined the samba school and see it as the continuation of the same organization.