A foreigner on a bad line (5)
I believe the answer is:
alien
'a foreigner' is the definition.
('alien' can be a synonym of 'foreigner')
'on a bad line' is the wordplay.
'on' is a charade indicator (letters next to each other).
'bad' indicates an anagram.
'line' with letters rearranged gives 'lien'.
'a' put next to 'lien' is 'ALIEN'.
(Other definitions for alien that I've seen before include "Foreign (from outer space?)" , "immigrant" , "exciting film based in space" , "Little green man, perhaps" , "movie!" .)