Sailor prodded by Rear Admiral waving flag in battle (9)
I believe the answer is:
trafalgar
'battle' is the definition.
(I know that Trafalgar is a naval battle)
'sailor prodded by rear admiral waving flag in' is the wordplay.
'sailor' becomes 'tar' (tar can mean a sailor).
'prodded by' is an insertion indicator (inserted letters prod their way into others).
'rear admiral' becomes 'RA' (naval abbreviation).
'waving' indicates anagramming the letters (letters wave around).
'in' means one lot of letters goes inside another.
'flag' anagrammed gives 'falg'.
'ra' placed within 'falg' is 'rafalg'.
'tar' enclosing 'rafalg' is 'TRAFALGAR'.
(Other definitions for trafalgar that I've seen before include "Public space in central London" , "Nelson battle and London Square" , "Cape" , "Eighteen zero five naval battle" , "Nelson's last battle" .)