Dont go to an English Soccer game if you want to feel Safe

At start of the 1906/07 season, a particularly ferocious encounter saw one player hurled against a metal advertising board. Millwall finished the game with only nine men, after the others were stretchered off following heavy tackles.

The East Ham Echo reported: "From the very first kick it was seen that there was likely to be some trouble. All attempts at football were ignored." The supporters were also criticised for fighting each other in the stands.

In 1926, when tough economic times were taking their toll on the docks, the rivalry turned nasty. The General Strike of that year was observed by workers in the East End, who were mainly West Ham supporters, but the Millwall-supporting shipyard workers of the Isle of Dogs refused to lend their support, provoking mass outrage.
...
In the 1960s, the two sides were again divided, this time by the arrival of London's two most notorious gangster families, the Krays and the Richardsons. The former were born and bred in the East End and supported West Ham, the latter were from south of the river and followed Millwall.

http://www.independent.co.uk/sport/football/news-and-comment/a-rivalry-that-dates-back-to-the-heyday-of-british-shipbuilding-1777732.html