I saw "Fever Pitch" sort of by accident; it was playing on the airplane going over to Europe. It actually wasn't half bad. Ben (Jimmy Fallon) is the world's #1 Red Sox fan, but his relationship with Lindsay Meeks (Drew Barrymore) may strain that. The movie is a fairly interesting look at how world events can affect peoples' relationships. It's especially eye-opening now that the Red Sox have ended their 80-odd-year losing streak. I guess that these sorts of things happen all the time and we just don't tend to notice them. Not too bad.
Another movie portraying an unusual relation to baseball is 2000's "Frequency". Check them both out.