Retired dude cheers sovereign for beginning vigorously (9)

I believe the answer is:

attacking

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'beginning vigorously' is the definition.
'attacking' can be an answer for 'beginning' (attacking is a kind of begining). I'm not sure about the 'vigorously' bit.

'retired dude cheers sovereign' is the wordplay.
'retired' is a reversal indicator.
'dude' becomes 'cat' (American slang for man, esp in Jazz).
'cheers' becomes 'ta' (both can mean thank you).
'sovereign' becomes 'king' (king is a kind of sovereign).
'cat'+'ta'='catta'
'catta' reversed gives 'attac'.
'attac'+'king'='ATTACKING'

'for' acts as a link.

Can you help me to learn more?

(Other definitions for attacking that I've seen before include "Assailing" , "offensive" , "Assaulting" .)

I've seen this clue in The Guardian.

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