In Argentina, not only do fans of opposing teams clash, but so do fans of the same team, as the main barra bravas have different factions that are constantly fighting for power.

These gangs are professional organizations that deal with large amounts of money, and normally consist of between 100 to 300 members.

One of the biggest groups, Boca Juniors' La Doce ("The Twelfth Man") -- whose leader, Rafael Di Zeo, was imprisoned in March -- is said to consist of around 2,000 members.

As Argentina's main national newspaper, Clarín, recently declared, "Not only do club directors and players fund the barra bravas, but so do celebrities and politicians." (Many clubs deny any association with the gangs.)

Most barra bravas have similar roles. On Sundays, they attend their club's matches and set the scene in the terraces, chanting for their team while creating an intimidating atmosphere for the opposition in the middle of the stands behind the goals.

But their roles change during the week. Some members of barra bravas are also well-paid employees of their club.