Basically exactly what's in the title. Berlin Olympics don't count since it occurred while there were tensions but WWII hadn't started yet(unless the Nazis were at war with someone already and I just forgot). US/USSR during the Cold War is a really fascinating read but I'm looking more at open warfare. I doesn't have to be a great power war or anything, but I'm mostly interested in overt action (So while Russia/Ukraine arguably count, I'm looking for more traditional conflicts)
If it has occurred, what happened? How did the fans interact with each other? How about the teams?
The 'blood in the water' water polo match took place during the 1956 Olympics in Melbourne. The USSR had invaded Hungary to put down an anti-Soviet popular uprising in October 1956. While the conflict was over by the time of the Olympics, approximately 250,000 Hungarians fled the country. The Hungarian water polo team were the reigning Olympic champions, and faced the Soviet team in December 1956. They beat the Soviets both literally and figuratively, while the crowd called for their heads. The match was cancelled with a minute left to play, with the win awarded to the Hungarian team, many of whom sought asylum in the West after the Olympics.