In regret, go back for scamp (5)
I believe the answer is:
rogue
'scamp' is the definition.
(thesaurus)
'in regret go back' is the wordplay.
'in' is an insertion indicator.
'regret' becomes 'rue' ('rue' can be a synonym of 'regret').
'back' shows that the letters should be reversed in order.
'go' backwards is 'og'.
'rue' going around 'og' is 'ROGUE'.
'for' is the link.
(Other definitions for rogue that I've seen before include "Deceitful and unreliable scoundrel" , "Baddy" , "Rapscallion" , "Bad person" , "Dishonest chap; solitary (elephant)" .)