The scenes that followed England's 1-1 draw with Russia shocked the football world and beyond.
England admittedly have a dark history of hooliganism, but few of their fans will have ever seen anything quite like what occurred inside the Stade Velodrome in Marseille before.
It was a dark day for football, but what is even more concerning is that it could be just the start of something much more dangerous.
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Russia is set to host the 2018 World Cup. Even prior to the latest violence, that had already prompted complaints because of racist incidents in the Russian league. Now, serious questions are being asked about whether it is safe to hold the World Cup there.
The Guardian quoted a tweet from Igor Lebedev, a Russian MP and football official, that is also worrying:
"I do not see anything terrible in fighting fans. On the contrary, well done, our guys. Keep it up!"
Many have been concerned by the quote showing such a lack of remorse. If Russia are to go ahead with their plans to host the World Cup, they need to demonstrate that they won't tolerate violence in 2018, let alone encourage it.
For the safety of players and fans from all over the world, hopefully this will be the final straw and something will be done to ensure there can't be a repeat of these scenes.
Russia and England have both been warned about their fans' behaviour and both teams have been threatened with disqualification from the tournament, and it's not surprising.
Football fans have travelled across the world, paid for flights and accommodation, gone to watch their country, fearing that they won't return home. If action isn't taken soon, the ugly side of the beautiful game will continue.
How should UEFA punish fans' behaviour? Have your say in the comments.