One critical thing to remember: the New York Yankees and Boston Red Sox are natural arch-enemies. They are like a mongoose and a cobra, like Batman and the Joker. There is no reconciling them whatsoever.
Vulgar chants about the opposing team will erupt during home games, without that team even being there, just because they hate each other so much. Vendors outside one team's ballpark will sell T-shirts alleging unnatural sexual practices by the stars of the opposing team*.
And a fan of one will never say anything remotely complimentary, or even fair, about the other. (See post above.)
Understand this, and you will understand much about baseball in America.
* Actually, I've only seen this in Boston. Draw what conclusion you will from this.