The Italian Football Federation has suspended all matches indefinitely after a policeman was killed as violence flared during a Serie A match between Catania and Palermo.
The trouble spread outside the stadium, and was most intense after the game finished more than half an hour later than scheduled.
Officer Filippo Raciti died when a home-made bomb exploded in his face.
A minute's silence had been observed before the match in memory of Ermanno Licursi, a club official who died last Saturday after being attacked while trying to break up a fight at an amateur league match in the southern town of Luzzi.
The federation has also cancelled Italy's international friendlies: a senior match with Romania on Wednesday, and an under-21 game against Belgium on Tuesday.
Commissioner Luca Pancalli said they will set up a commission to probe the link between sport and politics.
About 100 people were wounded, between officers and fans, in clashes led by hooded rioters who hurled fireworks and lashed out at police with makeshift weapons.
Police said they arrested nine people and had detained 23 others.
After the match, fans continued to fight running battles with police on the streets outside the stadium.
Around 100 people were treated for injuries, while dozens with lesser injuries were taken to local hospitals.
