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.

https://en.wikipedia.org/wiki/Ultras

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

https://www.reuters.com/world/europe/curva-nostra-mob-infilt...