Who is the protagonist and antagonist of the book Staying Fat for Sarah Byrnes?

Eric "Moby" Calhoune and Sarah Byrnes are the protagonists
in the story, with the emphasis on Eric, as Sarah is in a mental hospital and catatonic
for a significant part of the story.

As Sarah has been
hospitalized, her best friend Eric has to try and find out what has caused her mental
illness and possibly find a way to help.  They are aided along the way by friends and
some family and teachers at Eric and Sarah's school.

Virgil
Byrnes is Sarah's father, and he is the clear antagonist.  Later in the story, it comes
out that Virgil had abused Sarah when she was younger, and that her mental illness is
actually a cover because Sarah has become increasingly afraid that her mentally unstable
father might try to kill her.