Knock at small nail (6)

I believe the answer is:

attack

'knock' is the definition.
(I know that attack is a more specific form of knock)

'at small nail' is the wordplay.
'small nail' becomes 'tack' (I've seen this before).
'at'+'tack'='ATTACK'

(Other definitions for attack that I've seen before include "Strike" , "act of aggression" , "Set upon" , "Launch an offensive" , "Raid" .)

I've seen this clue in The Sun.

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