Commander has simple beef (8)
I believe the answer is:
complain
'beef' is the definition.
(I know that beef is a more specific form of the action complain)
'commander has simple' is the wordplay.
'commander' becomes 'com' (I've seen this in other clues).
'has' is a charade indicator (letters next to each other).
'simple' becomes 'plain' (similar in meaning).
'com'+'plain'='COMPLAIN'
(Other definitions for complain that I've seen before include "Bemoan" , "Grumble, moan" , "Remonstrate" , "Bellyache" , "Lament" .)