Permissible to run away! (5)
I believe the answer is:
legit
I believe this clue is a double definition.
'permissible' is the first definition.
(thesaurus)
'run away' is the second definition.
(as in 'leg it')
'to' acts as a link.
(Other definitions for legit that I've seen before include "In accordance with the law (abbr)" , "Authorised" , "Conforming to the law" , "not unlawful" , "Such theatre" .)