Criticism of one at the door? (5)

I believe the answer is:

knock

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'criticism' is the definition.
(knock is a kind of criticism)

I can't explain the rest of the clue.

(Other definitions for knock that I've seen before include "Disparage - seek admittance" , "Thumping in engine" , "Setback; thirteen across" , "Unfairly criticise" , "Bump" .)

I've seen this clue in the Evening Standard.

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