Masked protesters set bins on fire and threw rocks and glass bottles at police who responded with foam bullets in a street near Barcelona's Camp Nou stadium as Barcelona and Real Madrid faced off Wednesday in the first Clasico of the season.
Forty-six people were lightly injured in the clashes, including eight who needed to be taken to hospital for extra care, local emergency services said.
Nine people were arrested, Catalonia's regional police force said. They face charges of affront to authority and causing public disorder.
The protesters, many of them carrying Catalan separatist flags, began setting up barricades in the middle of the street, which they then set on fire after police arrived in dozens of vans, according to an AFP reporter at the scene.
Demonstrators rocked a police van and took down street signs that they added to the barricade, while some people sought shelter inside a bar.
Calm returned to the street as fans began to leave the stadium at the end of the match, which ended in a 0-0 draw.
Police closed the south exits of the stadium leading to the street where the clashes took place and asked fans to leave the venue through the north exits for "security reasons".
These were the first violent incidents in Catalonia since October when Spain's top court jailed nine Catalan separatist leaders over their role in a failed 2017 bid for independence, triggering days of protests that sometimes ended in clashes with police.
The original fixture in October had to be postponed due to the violent demonstrations across the wealthy northeastern region.
Inside the stadium thousands of fans held up blue banners with the words 'Spain, sit and talk' which were given to supporters outside the grounds and also carried the words, 'Freedom, rights, self-determination', as well as the slogan of Democratic Tsunami, the protest group promoting the cause of Catalan independence that organised the demonstration.
Protesters had begun gathering at the four corners of the stadium, blocking traffic, four hours before kick-off. Nearly 5,000 people surrounded the stadium, according to police.
Many protesters were carrying Catalan separatist flags
Twelve people were injured in the clashes
Nearly 5,000 people surrounded the stadium