Fan protests at an Italian top league game between Genoa and Siena led to a 45-minute halt in play as attempts were made to restore order.
Supporters of relegation-threatened Genoa, trailing 4-0, threw flares onto the pitch and climbed safety barriers.
Some even demanded that Genoa players take off their team shirts.
Observers said scenes were reminiscent of trouble at the same stadium in 2010, when clashes between fans and police halted an Italy-Serbia international.
Genoa, who are threatened by relegation in Italy's Serie A, were 4-0 down at the start of the second half when the trouble kicked off.
Referee Paolo Tagliavento halted play after home fans threw flares and smoke bombs onto the pitch.
Families with young children were reportedly forced to flee.
The visiting team retreated to the dressing room until the situation calmed down.
One report said Genoa team capital Marco Rossi went up to the "Ultra" fans behind one goal to appeal for calm, while many home supporters left the ground in disgust at their team's performance.
The game eventually resumed without incident, and Siena won 4-1 after an own goal.
Italian football federation chief Giancarlo Abete called the violence "unacceptable".
"Those are not fans. I hope these people are identified and condemned. They should not be allowed into the stadium ever again."
The Genoa president, Enrico Preziosi, said: "I'm sorry that 60 or 100 people can say and do as they want with impunity without us having the ability to control them and send them home."