Blockhead indisposed in attacking (9)

I believe the answer is:

assailing

'attacking' is the definition.
('assail' can be a synonym of 'attack')

'blockhead indisposed' is the wordplay.
'blockhead' becomes 'ass' (I've seen this in another clue).
'indisposed' becomes 'ailing' (synonyms).
'ass'+'ailing'='ASSAILING'

'in' acts as a link.

(Another definition for assailing that I've seen is " What pirates may be doing".)

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

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