This happens all the time that supporters of different teams clash, no matter if it is in any European competition like Champions League, UEFA cup or Conferance league or just i the regular leagues (Ligue, Bundesliga, etc.).

No long ago fans of AEK Athens clashed with fans of Dinamo Zagreb and in those clashes fans of AEK stabbed and killed one of their own. Despite they say this is not true police already did dna and one of the 2 knives used was from someone related to Original 21 (AEK’s ultras/hooligan group) while the other knife that was used was from a Panathinaikos fan who was recently released from jail Greek department of justice said. Dinamo fans are still in prison despite they are not guilty of manslaughter and Greek goverment even demanded Croatian goverment to arrest anyone they (Greeks) suspect from being in Athens when it happend (even guys who were in Zagreb the moment this fight happend got arrested in Croatia).

Here a link: https://www.ultras-tifo.net/news/7308-police-arrested-main-suspect-for-murder-of-aek-fan-it-s-not-croat.html

So OP you going to make this posts every week?

• Dotmund/Köln clashed twice with Schalke and also with BMG.
• Biris Norte (Sevilla) attacked a family birthday party of an United Family (Betis) member.
• Bulgaria vs. Hungary was full of riots outside the stadium because Bulgarian ultras united against the corrultion that takes place within the Bulgarian football association.
• Besiktas had a small clash with Galatasaray and stole ome of their banners.
• Lazio vs. Roma had clashes between both groups inside the stadium.
• and the list is long. I do not thing these posts you make are good for the sub and without actually knowing what happend and what is going on there is no point in having a discussion.