Permitted line very bad (6)
I believe the answer is:
lawful
'permitted' is the definition.
(I've seen this before)
'line very bad' is the wordplay.
'line' becomes 'l'.
'very bad' becomes 'awful' (I've seen this before).
'l'+'awful'='LAWFUL'
(Other definitions for lawful that I've seen before include "Licit" , "Not illegal" , "Legally permitted" , "Allowed" , "Legitimate" .)