In Santiago the most popular teams are Colo-Colo and Universidad de Chile (my team). Both teams are fiercely rivals and in their matches is very common to happen some violent brawls (thats why their matches are before noon). I think Colo-Colo is more popular but its probably 40% Colo-Colo and 35% Universidad de Chile.
But in my commune (it's like a Borough) another team gets and it's Universidad Catolica (UC). UC is associated with the upper classes (and its catholic/conservative tendencies) and UC fans are probably 30% of the people, (along with 30% for Colo-Colo and Universidad de Chile) here.
An important thing to say is that
Los de Abajo (Those from below, the Universidad de Chile's supporters group) is, unlike Colo-colo and UC's supporters, explicitly left-wing (this is a typical song with some interesting pictures:
https://www.youtube.com/watch?v=7GeniVlCl5E )
