The video of the stop (showing the police were in no reasonable danger) and the killing was widely circulated online, and drew a ton of anger and discussion of police brutality. While the officer who killed the kid is being investigated for "voluntary manslaughter," people are still angry, and the French have a reputation for protests and rioting when they get angry.
Multiple countries including the UK and USA have warned their citizens to stay away from affected areas in France. Persan Beaumont town hall, Paris region sacked and burned down. But a lot of people are saying this could spread across europe. It's not about a teen killed by police. It's about something that's been about to boil over anyway and any incident could set it off.
In unconfirmed news, the Holocaust monument was desecrated.
France has had riots earlier this year on increasing the pension age by Macron. But this energy and boiling over feels different.