I've only read edited Gibbon and limited other references and they never got specific about it that I read, but when I think about it for a second, it seems very likely that rabid sports fans of a very practical militaristic sport might often have more physical and professional ties to it than just as sports fans or partisans by accident or tradition. It also makes sense out of the brother against brother rivalry alluded to, if people's real jobs and/or semi-military gangs are involved....if career, ambition, social status come into it, not just cheering a side and random hooliganery.