Protagonist vs. Antagonist

What is the primary motivation of the protagonist & antagonist?

I wouldn't really say that the play has a protagonist and antagonist per say.

First of all, let me explain what protagonist and antagonist mean:
Protagonist >> the main character >> often referred to as "The hero"
Antagonist >> opposition against which the protagonist must contend >> often referred to as "The villain" 


Therefore, I am really not sure that this play does have a typical protagonist nor antagonist. Well, Dodge seems to be the protagonist of this play. He kept the farm alive, he took care of his family, he kept the big secret, etc. Although he is old and drinks alcohol and smokes a lot, he is kindhearted and actually a good person. As a matter of fact, yes, he is the protagonist of this play. He appears to be in the middle of everything as well as one of the most important characters. However, I cannot really say who is the antagonist. Maybe Tilden, the oldest son who had incestuous affair with his mother. After all, he was the one to kind of ruin their family. I'm not saying it was only his fault. Also the mother should be smarter. But, it seems to me that Tilden is the antagonist.

The critical thing that they have in common, is that it is a father and a son. Which is kind of crazy, because as I said protagonist is like a hero whereas antagonist is like a villain. Therefore I think it is a little bit crazy that father and son have such relationship. However, it is not uncommon. Another really messed up thing is that Tilden [son] had an affair with his mother [Halie]. This gives a reason to Tilden be the antagonist and Dodge [father] the protagonist. Another reason is that Tilde was supposed to be a football star. However, he ended up being almost arrested and banned from one state. To sum it up, he was expected to do big things in his life.