Following widespread looting sprees and acts of violence occurring on the sidelines of the October 17 student protests, so-called “casseurs” seem to be the centre of attention. But the term, which comes from the French verb casser or “to break”, poses more questions than answers. The sociologist Paolo Stuppia examines the unprecedented situation many cities across France are having to contend with, and the complex combination of collective action whose motivations are unclear and the social media’s extreme agility.