The Popular refers to the area in the ground where the ultras and more vocal fans stand and they ask players to leave everything on the court to win
Lyrics
Let's see if we understand, The players and The Popular, You kill each other on the field, That here in the stands are going to encourage, Put more b*lls, Put more heart, How to place ourselves in the plank, We left everything, Just to see that shirt. Put more b*lls, Put more heart, Because this is River and we have to be champions, Come on "Millo", Not fail all your people...