A group not bothered about chaps leaving (11)

I believe the answer is:

abandonment

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'leaving' is the definition.
(abandonment is a kind of leaving)

'a group not bothered about chaps' is the wordplay.
'a group' becomes 'aband' (I can't justify this - if you can you should believe this answer much more).
'bothered' is an anagram indicator.
'about' is an insertion indicator.
'chaps' becomes 'men' (I've seen this before).
'not' with letters rearranged gives 'ont'.
'ont' going around 'men' is 'onment'.
'aband'+'onment'='ABANDONMENT'

Can you help me to learn more?

(Other definitions for abandonment that I've seen before include "surrender" , "being neglected" , "Process of giving up completely" , "Act of desertion" , "leaving" .)

I've seen this clue in The Telegraph.

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