2 different types, sadly go under same banner.

there is a clear difference between:

a) Spontaneous and usually low level disorder caused by fans at or around football matches (the type that typically occurs at England away matches)

and

(b) Deliberate and intentional violence involving organised gangs (or 'firms') who attach themselves to football clubs and fight firms from other clubs, sometimes a long way in time and space from a match.

sometimes tabloid newspapers and news affiliates within the media have a tendancy to label both under the same title of hooligan. much like the sun newspaper did during the hillsbrough disaster.

definitions from here