Barcelona's ninth-round La Liga meeting with Real Betis boiled over amid a series of contentious refereeing calls.
Barcelona led 2-1 at the break, then stretched that advantage with a third goal in the 51st minute.
Betis hit back almost immediately. Abdessamad Ezzalzouli pulled one back for the Moroccan's side to make it 3-2 in the 54th minute.
Spanish newspaper "Sport" claim that goal should never have stood. Fermin Lopez had been fouled in the build-up, referee De Burgos Bengoetxea waved play on, and Ezzalzouli went one-on-one with Joan Garcia.
Hauled back, Lopez had gone to ground. Betis goalkeeper Alvaro Valles wanted him up and quickly once Ezzalzouli had scored, grabbing hold of the Barcelona man and shoving him towards his feet.
Lamine Yamal waded in to protect his team-mate, and Facundo Bernal went for him. What began as a scuffle ended with the Betis midfielder's hands around Yamal's neck.
Yamal wriggled free. Bernal responded by throwing a headbutt at him, and the referee saw the lot, producing a straight red for the Betis player once tempers had cooled.