I'm not following these protests closely, but aren't you going to have a minority of violent people in any protest? That's just the nature of argry, large groups.
If that's your bar for "violent protest", then it's trivial for anyone to disrupt any protest by injecting interlopers to try to trigger an explosion. There's evidence that undercover police tried to instigate violence and looting in the BLM protests. Couldn't that be happening here too?