Yes, pickpockets in Europe can be a problem, but they are very rarely violent. The goal is to be away before you're even noticed so if you keep watch over your stuff, that's plenty. It would be extraordinary for someone to use a weapon to mug someone like in the US. The reason being that basically nothing will happen for small theft and pickpocketing but police will actually investigate and judgest will sentence if there's a weapon involved so it's dumb from the criminal's POV to escalate as the risk/reward gets far less favorable.