BARCELONA ultras were involved in a violent street battle with their Valencia counterparts before Saturday's LaLiga match.
Chairs and flares were thrown as numerous objects were used as weapons right outside Los Che's Estadio Mestalla.
Local authorities believe the fight to have taken place between Barcelona's Boixos and Valencia's Yomus ultra groups.
Footage filmed by locals hiding in cafes and apartments opposite the stadium showed the vast number of people involved.
Plastic street barriers, poles, cones and even plates from streetside restaurants are seen being used as weapons before riot police close in and disband the fighting.
The clash occurred on Sunday morning ahead of the meeting between two of Spain's biggest clubs at 3pm.
Valencia's Yomus group were founded in 1983, two years after their Barcelona rivals formed up.
The Valencians have previously been linked with holding something of an anti-Catalan sentiment.
After going quiet in the early 2000s, Yomus has been a more common fixture at the Mestalla since the start of the last decade - situating themselves in the Curva Nord.
Likewise, Barca's Boixos group congregate behind the goal at the Camp Nou despite officially being banned from the ground.
Their initially close relationship with the club was abandoned by former president Joan Laporta, who threw the ultras out in 2003.
Earlier in the month, a group of Boixos fans were blamed for vile Nazi chants at a reserve derby with Espanyol.