Sport runs a bit deeper than just sport in Italy. There are a lot of political/social affiliations with certain teams. Probably related to that in some way.

To try and relate it to America, imagine if when Portland plays Dallas a portion of Dallas's fanbase travels to Portland together and are affiliated with Qanon or some ring wing group and they travel to Portland not just to support their team, but to antagonize members of Portlands supporter groups who are affiliated with antifa.

Luckily we do not have this in the US, but this is the state of soccer in Italy.