This does not surprise me, this is just the beggining. There will be alot more in the near future.
It is very common in society that when there are alot of unemployed people and times are hard... Riots start (or a war).
Specially during a football game where there are alot of men together. The adrenaline rush goes to your head as well as testorone levels in the air. Mix adrenaline with hard times with no money in your pocket, and you get = A Raging FIGHT!
It has happened before throughout history and it will happen again.
If you do not want to get involved in this sort of neantherthal ritual, stay home with
some friends, order a pizza and some beers and watch the game confortably from your
living room. Its cheaper and no bruises afterwords.