Incompetent fellow recruited by military division (5)
I believe the answer is:
unfit
'incompetent' is the definition.
(I've seen this before)
'fellow recruited by military division' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'recruited by' indicates putting letters inside.
'military division' becomes 'unit' (I've seen this in another clue).
'f' put inside 'unit' is 'UNFIT'.
(Other definitions for unfit that I've seen before include "In poor condition" , "Not healthy" , "Inappropriate" , "Incompetent" , "Ill - out of shape" .)