They normally have to ask for dates, permits, are normally driven by groups that have been around for long, they have websites, they have a list of asks, etc etc.
Compare that with violent ones that see the opportunity coming with 3-4d heads-up (because peaceful protests are normally covered with a little advance - 3-4d - by mainstream press), create an Instagram/TikTok/Whatsapp/Snapchat group, spread it aggressively thanks to zero cost of social/IM, and their only objective is to smash everything in their path (and if they manage, steal some loot to resell).
Compare that with violent ones that see the opportunity coming with 3-4d heads-up (because peaceful protests are normally covered with a little advance - 3-4d - by mainstream press), create an Instagram/TikTok/Whatsapp/Snapchat group, spread it aggressively thanks to zero cost of social/IM, and their only objective is to smash everything in their path (and if they manage, steal some loot to resell).