A friendly between AC Milan and Italian lower division club Pro Patria was suspended after players walked off because of racist chants, reports BBC Sport.
Milan's Kevin-Prince Boateng picked up the ball 25 minutes into the first half and kicked it into the crowd.
Ghana international Boateng then removed his shirt and was followed from Pro Patria's home pitch by both sets of players and officials.
There had been appeals for the abuse to stop from the public address announcer.
It was quickly established that play would not restart and AC Milan's official website said other black players in the Milan side - M'Baye Niang, Urby Emanuelson and Sulley Muntari - suffered abuse.
Milan coach Massimiliano Allegri told reporters: "We are disappointed and saddened by what has happened.
"Milan play for the right to respect all players. We need to stop these uncivilised gestures.
"We are sorry for all the other fans who came here for a beautiful day of sport. We promise to return, and we are sorry for the club and players of Pro Patria, but we could not make any other decision.
"I hope it can be an important signal."
Milan's organising director Umberto Gandini added: "It is so sad but we had to give a strong signal. Very proud of all Milan players for their decision. No other comments."