Don't punish defence (6)

I believe the answer is:

excuse

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'defence' is the definition.
(I know that excuse is a type of defence)

I can't explain the remainder of the clue.

(Other definitions for excuse that I've seen before include "Defense of offensive behavior" , "Allow to be released from a duty" , "Forgive - allow to pass - plea" , "Justifying explanation" , "Grant exemption or release to" .)

I've seen this clue in the Irish Times (Crosaire) and The Sun.

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