Five hard-core Napoli fans were arrested Wednesday on suspicion of blackmailing the Serie A club to get free tickets and keep their part of the ground a no-go area.
Police said the suspects hurled smokebombs and set fire to the San Paolo stadium's press box in order to intimidate the club during a match in December 2006.
The action, aimed at getting the ground banned, was a reprisal for being denied free tickets, police said.
The so-called 'ultras' also issued "serious" threats against a Napoli official in August 2007, police said.
"The group acted under iron-clad rules from their chieftains to exert a claim to their portion of the stadium as an extra-territorial zone, a private domain outside the rule of law and subject only to gang law," the police added.
The fans belong to a number of hooligan groups including the Blue Tigers, the Ultras 72 and the NISS - short for Niente Incontri Solo Scontri, "No Talks Just Clashes".
Italian ultra groups have often been accused of exerting undue pressure on clubs and even holding them to ransom - offering a Mafia-style 'protection' from violence.
