Asking for trouble.
I went to an Inter Milan match last year and sat in the Ultras, the police were all down the other end of the stadium, as far away from them as possible. The let them knock themselves out mentality is already there and it works most of the time, when the police wade in it amplifies the violence in most cases.
These Sicilian derbies are notoriously violent, this season is the first time in few decades that 3 of them have all been in the same division. A riot like this was almost inevitble, they could have had 10x as many police there and it would of still been total carnage
Siere A are just lucky Pisa and Fiorentina are divisions apart, thats another war waiting to happen.