Barra Brava

Members of barras bravas are scattered between the flags that they deploy. In the picture, barra brava of Club Atlético Nueva Chicago, from Argentina, in the middle of the crowd.
“Barra brava (lit. ‘fierce group‘) is the name of organized supporters’ groups of football teams in Latin America, analogous to European ultras and British hooligans in providing fanatical support to their clubs in stadiums and provoking violence against rival fans as well as against the police. … They also look to attack rival fans (especially rival barras bravas), which leads to fights with them (most of the time outside of stadiums before or after matches, but sometimes during them in the stands), and defend the rest of their team’ spectators from rival attacks (especially in away matches, where normally they are outnumbered by home fans) and police repression. These groups originated in Argentina in the 1950s and spread throughout the rest of Latin America.  … During the 1920s in Argentina, irregular groups of fervent fans spontaneously began to appear at football matches. These groups were denominated as barras by the media, a term that in Rioplatense Spanish slang is equivalent to the term gang, but in its original meaning (not necessarily associated to crime), that is ‘an informal group of people (usually friends) who meet frequently and usually do common activities’.  …”
Wikipedia
Barras Bravas: The Dark Side of Soccer (2015)
Guardian – The barra bravas: the violent Argentinian gangs controlling football (2011)
YouTube: River Plate Barra Brava – Best Moments, Why River Plate & Boca Juniors Hate Each Other: Boca vs River | Superclásico | Roots of the Rivalry
The Barras brava section of the stadium is recognizable for their flags, a characteristic unrivaled by other areas of the stadium has more quantity or density of such. In the picture, La Banda de Fierrois an organized supporter group of Gimnasia y Esgrima La Plata.