Prison rebel is turning reckless ... (13)
I believe the answer is:
irresponsible
'reckless' is the definition.
('irresponsible' can be a synonym of 'reckless')
'prison rebel is turning' is the wordplay.
'turning' indicates anagramming the letters.
'prison'+'rebel'+'is'='prisonrebelis'
'prisonrebelis' is an anagram of 'IRRESPONSIBLE'.
(Other definitions for irresponsible that I've seen before include "Unreliable" , "Thoughtless" , "Negligent" , "Nor caring about consequences" , "Wantonly careless" .)