I was at the Yankees-Red Sox game late last August (
August 28), and saw nothing bad from either side. Although, of course, I only witnessed whatever went on around the area I was in. There were a couple Red Sox fans cheering for them, but the Yankee fans didn't do anything to them.
Of course, that's not representative of the "rivalry" as a whole. Really, I'm sick of both "hardcore" Red Sox and Yankee fans. They each have these elitist standpoints and just try to belittle the opposing team when the fact of the matter is that BOTH teams are VERY good and VERY well run.
Sometimes, the Red Sox are better. Sometimes, the Yankees are better. Neither team is a bad team. I'm sorry for injecting some logic into the nonsense that is the Red Sox-Yankees rivalry.