Crossword Genius

They besmirch boneheaded groups (5)

Ross

I believe the answer is:

blots

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'they' is the definition.
Both the definition and answer are plural nouns.
Maybe they are linked in a way I don't understand?

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Another definition for blots that I've seen is " Stains, perhaps on copybook".)

I've seen this clue in the Evening Standard.
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