A 17-year-old Italian youth is being questioned by police in the Sicilian city of Catania over the death of a policeman in riots last week.
Post-match violence spilled out on to the streets around the stadium
Filippo Raciti died after violence broke out following a football match between rivals Catania and Palermo.
Reports say the youth was detained overnight on Tuesday along with three other people all under the age of 18.
Italian media said the teenagers had been identified from closed-circuit television footage of the clashes.
Mr Raciti, 38, was killed outside the city's Massimino stadium.
Although he was initially believed to have died when a home-made bomb was hurled into his vehicle, a post-mortem examination revealed that a blow from a blunt object caused the injuries which killed him.
Police had made a total of 34 arrests, including 11 minors, but none of these was directly connected with the death of the police officer.
Mr Raciti's death prompted outrage from Italian politicians, the suspension of all amateur and professional games and a call for an urgent overhaul of the country's stadiums.
After a meeting in Rome, the interior ministry said it would reopen just six of the country's stadiums - the only ones to meet newly-introduced safety standards.
Catania's Massimino stadium and Milan's San Siro stadium are among the 25 venues that will remain closed to spectators.
Football matches will be played behind closed doors and night matches have been banned.