Somewhere between dedicated fans of (often working class) European Football teams and paramilitary organisations. Green Street starring Elijah Wood is a film accessible to overseas audiences detailing the cultural phenomenon n the UK.
In Europe however, Italy in particular, organised crime is embedded in the structure - e.g. Gennaro Di Tommaso aka "The C0rpse", the leader of Napoli's ultras whose approval is needed before a match can take place