AC Milan players walked off the field because of racist chants, abandoning an exhibition match in the first half with lower division club Pro Patria on Thursday.
The game was interrupted and later ended because of chants directed at several black Milan players, despite appeals to stop from the public address announcer.
After repeated chants directed his way, Ghana midfielder Kevin-Prince Boateng picked up the ball and kicked it at a section of the crowd in the 26th minute of the first half.
"Walking off was the right choice when faced with something like this," Milan coach Massimiliano Allegri said. "We need to stop these uncivil gestures. Italy needs to improve and become better educated and more intelligent."
Boateng said on Twitter after the game: "Shame that these things still happen... #StopRacismforever."
Anti-racism campaigners praised Boateng for walking off the field in protest.
Piara Powar, executive director of European anti-discrimination group FARE, demanded strong action from the Italian FA.
"We salute Kevin-Prince Boateng for his actions and his teammates for their support," Powar told Press Association. This is the not the first time a player has walked off in Italy - if the situation continues it may not be the last.
"Italy, as much as any country in Europe, has a serious problem of racism to deal with. Football infrastructure is in need of renewal and at serious odds with the changing nature of Italian society. We look forward to strong action by the (Italian football association)."
Italian association president Giancarlo Abete branded the incident "unspeakable and intolerable" and an offense to Italian football and announced an immediate inquiry.
"No sanction or measure can erase the disdain for an unspeakable and intolerable episode," Abete said in a statement on the Italian FA website. "We must react with force and without silence to isolate the few criminals that transformed a friendly match into an uproar that offends all of Italian football."
The match, which was scoreless at the time, was not resumed. The game was played in Busto Arsizio, a town located north of Milan. Pro Patria plays in Italy's fourth-tier division.
Milan said on its website that the insults came from a small group of Pro Patria fans, adding other supporters disassociated themselves from the chants.
Milan, returning from its holiday break, is preparing to play Siena on Sunday.
Information from The Associated Press and Press Association was used in this report.