In 1998, in a Bristol city centre pub, after a young French student cheered on his country's team during the televised World Cup final - they won - he was followed outside and set upon by a bunch of thugs who fractured his skull and left him in a coma. He was flown home in an air ambulance and later on when he was out of danger the mayor of Bristol went over to see him to apologise on behalf of the city.
The same year, a large number of England fans visiting France for the World Cup ran amok in Marseille, trashing a large part of the Old Quarter near the harbour. One guy when arrested said he did it "for England". Another, a Royal Mail manager was jailed for three months.
A couple of years ago a man went into a Bristol pub wearing a Bristol Rovers scarf, and was attacked by some Bristol City fans. He later died.
This sort of thing happens disgracefully often.