Midge has unexpected tang (4)
I believe the answer is:
gnat
'midge' is the definition.
(I've seen this in another clue)
'unexpected tang' is the wordplay.
'unexpected' indicates an anagram.
'tang' is an anagram of 'GNAT'.
'has' acts as a link.
(Other definitions for gnat that I've seen before include "small irritant" , "Woodland area" , "Tiny biting insect" , "a little bit of a nuisance" , "Small biting flying insect" .)