As someone living in Barcelona I can tell you that the majority of violence was caused by the Police starting to go after protestors, police provoking protestor

As someone living in Barcelona I can tell you that the majority of violence was caused by the Police starting to go after protestors, police provoking protestors with Spanish flags, playing the Spanish national anthem. Its was caused be a few people who always cause violence, does not matter if its a soccer game or a peaceful protest. It was caused by the central government spending years changing the law, to the point where its illegal to protest the government, unless they authorize it. Its caused by police stopping and searching people daily on the streets, confiscating anything that can hide your face, and Catalan flags. There are even cases where Spanish police officers sent to catalunya from other parts of spain have been identified with swastika tattoos. There is a HUGE issue, where people on both sides have been abusing the system for their own gains. Both political sides know that as long as they can keep the people fighting and "hating" each other, they can continue with the corruption that exists here.