Pecsi MFC and Cibalia fans clashed on the pitch during a friendly match in Hungary on Saturday.
Cagliari and Pogon Szczecin hooligans clashed in the streets of the Sardinian capital after a friendly between the two sides on Friday.
A brawl erupted between Nantes and Brest fans immediately after Friday's pre-season friendly at the Mane Braz stadium in the north-western French town of Inzinzac-Lochrist.
Around 50 fans began fighting on the pitch at half-time during a game between former players of Club America and Pumas UNAM at Eddie West Field in Santa Ana on Sunday.
Sporting fans were attacked by fans from Spain before the match.
Swedish police arrested about 100 Brøndby fans in Malmö.