Greek police arrested more than 50 people on Monday suspected of being involved in organized hooligan gangs linked to the death of a police officer during riots at a volleyball game in December.
The 31-year-old officer was on duty when he was hit by a flare at the top game between Olympiakos Piraeus and Panathinaikos Athens when hundreds of violent fans rioted. He died 20 days later.
An 18-year-old was arrested for allegedly throwing the flare but Monday's major raid was a bid to clamp down on organized hooliganism at volleyball, football and basketball games in Greece.
The death was the final straw for Greek society in terms of fan violence in sport, government spokesman Pavlos Marinakis told journalists on Monday.
Following the death of the officer, the government closed arenas to all fans for two months.
New rules are now in place which include football supporters having to register their identification before buying match tickets.