Lots of terrible examples to go around across the globe. A few years ago a woman who is a fan of the University of Alabama football team murdered another woman who was a fan of the same team. Why? Because the victim wasn't upset enough about the team they were both fans of losing a game earlier that day. So being a rival isn't even required for violence to happen. Heighten emotional states are inherently unstable.

People are being killed "routinely" for European football? That's simply ludicrous.

Yes, in Poland alone there has been ~one death every year.

2001 Opatów, 2003 Walichnowy, 2007 Kielce(knifed), 2007 Łódź(coma), 2011 Poddębice, 2011 Kraków, 2018 Prokocim(arm cut off with machete, body massacred with baseball bats, axes and hammers). Thos eI could find with a quick google.

Example clip from one https://www.youtube.com/watch?v=jKXOsC3ms7k train was emergency stopped in the middle of nowhere, other team was already waiting after being transported by shuttle buses. You can search "Ustawka" on YT for more.

7 deaths in 17 years is not routine.

This article https://krakow.onet.pl/krakow-wojna-gangow-lata-ktore-niosly... found 15 killings between 2002-2018.