Any restriction on back will irritate (5)

I believe the answer is:

annoy

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'irritate' is the definition.
(I know that irritate can be written as annoy)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for annoy that I've seen before include "Irritate, nettle" , "Nark - nettle" , "Upset" , "Irritate - pester" , "Make slightly angry" .)

I've seen this clue in the Sydney Morning Herald.

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