Internacional captain Andres D'Alessandro and his Gremio counterpart, Maicon Souza, needed to be restrained by officials from going after each other during the coin toss before their Brazilian city derby.
The two players had a heated exchange in the prematch protocol for Sunday's league game at Porto Alegre's Bela-Rio stadium.
They refused to shake hands and Argentine midfielder D'Alessandro twice had to be restrained by an official after making aggressive moves towards Maicon.
The "Gre-nal", the nickname given to the derby between the sides, is among the fiercest of rivalries in South America. Gremio won the encounter 2-1.
Sunday's derby will also be remembered for being the first Clasico to have video assistant referees (VAR) tested in Brazilian football. Its usage was considered "positive" by the operators.
The Brazilian Football Confederation (CBF) are keen to implement the system in the country's top flight but the clubs last month voted against it.