A wild dog doing badly (5)
I believe the answer is:
dingo
'a wild dog' is the definition.
(dingo is a kind of wild dog)
'doing badly' is the wordplay.
'badly' indicates anagramming the letters (letters in the wrong order).
'doing' anagrammed gives 'DINGO'.
(Other definitions for dingo that I've seen before include "One running wild in Australia" , "Wild thing" , "Kipling's "Yellow-Dog"" , "Want a dog" , "dog running wild" .)