Eintracht Frankfurt fans clashed with police on Wednesday after arriving in Naples despite not having tickets for their team's Champions League decider with Napoli.
Footage broadcast by Italian media showed hundreds of supporters of the German club throwing smoke bombs and flares at police, who responded with tear gas.
A police car was also set on fire as chairs, bottles, and metal poles were thrown by hooded men dressed in black.
They travelled to southern Italy even though Eintracht decided against selling tickets for the away section at the Stadio Maradona for the second leg of the last 16 tie.
Eintracht didn't take up their allocation after the Naples prefecture decided on Sunday to ban residents of Frankfurt from buying tickets for the match.
On Saturday, an initial ban on Eintracht fans, imposed on Friday by the Italian interior ministry which targeted all people residing in Germany, had been overturned.
Sunday's decision came after violence in the first leg won 2-0 by Napoli in Frankfurt, which led to nine people being taken into custody.
Eintracht fans have been under close surveillance by European governing body UEFA since the pitch invasion which greeted the club reaching the final of the Europa League, eventually won by beating Rangers.
They also clashed with Marseille fans in September, with both sets of supporters lobbing smoke bombs at each other and one Eintracht fans being seriously injured.