Reversed decline taking over American support (8)
I believe the answer is:
espousal
'support' is the definition.
(thesaurus)
'reversed decline taking over american' is the wordplay.
I cannot quite see how this works, but
'over' could be 'o' (cricket abbreviation) and 'o' is found in the answer.
'american' could be 'usa' and 'usa' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for espousal that I've seen before include "Acceptance with approval" , "old-fashioned marriage" , "Action of adopting (a cause)" , "Favourable reception" , "championship" .)