You have to love soccer in Mexico. Deadspin gives us the play by play:

A Cruz Azul fan takes the field after his team goes down by three goals. He approaches Gerrardo Torrado with sarcastic salutations. Torrado ignores him. Fausto Pinto pushes the fan away. Christian Giménez then enters the conversation with a flying side kick and a general beating. The fan throws a punch to defend himself. Amazingly, the Morelia players intervene in an attempt to save the fan. The two teams begin fighting. The Cruz Azul goalkeeper, Jesus Corona, almost knocks out a Morelia coach with a vicious headbutt.

via Deadspin