What I want to suggest I don't know if it can be possibly practiced but i know that if it's being practiced, it can stop the repeatedly fighting and what I want to suggest is that the stadium should have a barricade to seperate both fans from sitting next to each others. The stadium should be divided into two parts and let the fans of each team occupy their seperate parts and should not be allowed to go to the sits of the fan of another team. If fans of the different teams can be kept separately, it would stop the fight, maybe after the match they can fight outside the stadium.
This is easier said than done. Seats are usually chosen by people not because they are supporting a team, but because they want to get a better view of the game. If the organizers were to implement this, how about those non-hardcore fans who just want to watch the game? They will be given seats that are not ideal for viewing, or somewhere they wouldn't get their money's worth.
@dothebeats, I know it's more easy to say than to practice it but I know for a truth that if there's separation of fans sitting position at the stadiumstadium it would lead to all fans of one team to only stay on their own side and never cross over to the side of the other fans. These would hardly be done because at the stadium you can't tell people where to sit and where not to sit but if there's determination to do it, they will start gradually to practice it. They should place a label saying that only the fans of team A should stay that side and also another label saying that fans of team B should go over to that side.