One of the world’s most-watched soccer matches was played amid heavy security Wednesday night as the Spanish authorities sought to keep Catalonia’s separatist movement from disrupting the game between host Barcelona and Real Madrid.

While the game in Barcelona’s Camp Nou stadium began without incident, some riot police clashed with protesters in the streets outside, and plastic trash cans were set on fire.

The match, which drew nearly 100,000 spectators and ended in a 0-0 tie, was halted briefly when a few dozen balls were thrown onto the field, some of them bearing a message urging the Spanish government to open a dialogue with the separatists.

Thousands of police and private security guards were deployed in and around stadium. During the street clashes, riot police used batons to force back the crowd. Some protesters also fought between themselves, while others threw objects at police officers lined up behind shields. At least four trash cans were set on fire, and a smell of smoke wafted into the Camp Nou ahead of the game.