Action taken by fine Italian in good shape (8,3)
I believe the answer is:
fighting fit
'in good shape' is the definition.
('fighting fit' means fit and healthy)
'action taken by fine italian' is the wordplay.
'action' becomes 'fighting' (military action).
'taken by' means one lot of letters go next to another.
'fine' becomes 'f' (abbreviation).
'italian' becomes 'it' (abbreviation for Italian).
'fighting'+'f'+'it'='FIGHTING FIT'
(Other definitions for fighting fit that I've seen before include "really healthy" , "In great form" , "very well" , "In excellent health" , "Standing up to attack of illness" .)