Former British soldier, or cadet in need of training (7)
I believe the answer is:
redcoat
'former british soldier' is the definition.
(I've seen this before)
'or cadet in need of training' is the wordplay.
'in need of training' indicates anagramming the letters.
'or'+'cadet'='orcadet'
'orcadet' with letters rearranged gives 'REDCOAT'.
(Other definitions for redcoat that I've seen before include "One employed to entertain" , "British soldier (hist.)" , "Tommy, once" , "British soldier in the American War of Independence" , "British soldier and holiday camp worker" .)