The Taser is currently being trialled in 12 Italian cities, and its first use was in Florence.
The electric stun gun was fired at a 24-year-old homeless Turkish man who was behaving aggressively and shouting threats on Tuesday evening.
According to Italian news agency ANSA, the man, who was completely naked, punched two other homeless men and resisted restraint before being stunned by police.
He was arrested and transferred to the psychiatric ward of Santa Maria Novella Hospital, from which he had previously been discharged on September 3.
Aside from the Tuscan capital, Tasers are being trialled in Bologna, Brindisi, Caserta, Catania, Genoa, Milan, Naples, Padua, Palermo, Reggio Emilia and Turin.
The trial began on September 6 and will continue for three months.
Italian authorities will then decide whether to implement it in other cities across the nation.