Varsity men playing for Chelsea? (5)

I believe the answer is:

blues

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'varsity men' is the definition.
The definition and answer can be both animals as well as being plural nouns.
Perhaps you can see an association between them that I can't see?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for blues that I've seen before include "State of depression" , "Jazz classic (2,5,5) - See 9" , "US music style" , "Feeling of sadness or depression" , "Depression - music" .)

I've seen this clue in the Evening Standard.

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