Football originated as a peasants game which was violent, boozy and had very few rules. It was more traditionally played by the working class. Though it has changed a lot for the better, there are still a minority who still like that aspect, and if they're not good enough to play then they will conduct their own mob football on the streets (just without a ball). Rugby for example, grew up in a posh school which not only had strict rules but also a code of conduct befitting gentleman. It was less accessible for the working class. The moral etiquette extended off the pitch as wel, which is I think why Rugby fans tend to be far better behaved. I would also say that percentage-wise, Rugby fans are probbaly more affluent/educated/refined than most football fans. A stark genralisation, but that is the feel I get from watching both sets of sports fans.