This seems like a strange discrepancy. Why is this the case? Maybe it is because "favorite team" is clearly singular, and is closer in the sentence to the "is"/"are" then the plural indicating sound in "Red Sox". Or maybe it is just whichever comes first which determines how the "to be" is conjugated?
Hm, but what if instead of connecting a noun phrase (determiner phrase?) like "The Red Sox" to another noun phrase (determiner phrase) "John's favorite team", we instead connect it to an adjective?
"The Red Sox are singular.", "The Red Sox is singular.", "Singular is The Red Sox." "Singular are The Red Sox." . Well, the "[Adjective] is [noun]" is kind of an unusual thing to say unless one is trying to sound like one is quoting poetry or yoda or something, but to the degree that either of them sound ok, I think "Singular are The Red Sox." sounds better than "Singular is The Red Sox." . Though, in this case, there doesn't seem to be anything grammatically suggested by the adjective that the thing be in the singular case (maybe I shouldn't have used "singular" as the adjective..) .
Hm, what if instead of "John's favorite team [is/are] the Red Sox." , we instead look at "John's favorite [is/are] the Red Sox." ? In this case, it seems, less clear which is more natural? They seem about the same to me (but that might just be me, idk.) .
Anyway : Weird!
I actually think this could extend to a lot of situations where the object is referring to a single group, not just plural-sounding proper nouns. Like if asked "what was your favorite zoo exhibit?", I would probably respond "my favorite was the giraffes" not "my favorite were the giraffes". I'm actually not even sure what the correct response would be technically though. "My favorites were the giraffes" implies multiple favorites, and "my favorite was the giraffe" makes it sound like the exhibit had a single giraffe. So it feels like subject/object have to mismatch then.
In English: It's only five minutes to the bus stop.
In German: Es sind nur fünf Minuten zur Bushaltestelle. (It are only five minutes to the bus stop.)
I think it's a question of whether the verb is supposed to agree with the subject or the complement.
interesting. to my (non-native) ears, the second sounds more natural. Wonder how common preference for each of those is.