Denies rot about court martial offence (9)

I believe the answer is:

desertion

I'm a little stuck... Click here to teach me more about this clue!

'court martial offence' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'denies rot about' is the wordplay.
'about' indicates an anagram.
'denies'+'rot'='deniesrot'
'deniesrot' is an anagram of 'DESERTION'.

Can you help me to learn more?

(Other definitions for desertion that I've seen before include "Abandonment" , "going AWOL" , "flight" .)

I've seen this clue in The Daily Express.

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