Tough rogue behind tart (4-6)
I believe the answer is:
hard-bitten
'tough' is the definition.
('hard-bitten' can be similar in meaning to 'tough')
'rogue behind tart' is the wordplay.
'rogue' indicates anagramming the letters.
'behind'+'tart'='behindtart'
'behindtart' anagrammed gives 'HARD-BITTEN'.
(Other definitions for hard-bitten that I've seen before include "Cynical and ruthless" , "Tough, cynical" .)