According to Italian news agency ANSA, he made a fascist salute at the city's war memorial before being arrested by police.
Photos from the scene show a man being put into a police car, wearing an Italian flag draped over his shoulders.
Macerata's Mayor Romano Carancini said six people - five men and one woman, were injured. One of them is in a serious condition.
All of those injured were foreigners, police confirmed, and Mr Carancini said they were black immigrants.
SKY News.