A bumpkin of a sort (3)
I believe the answer is:
oaf
'a bumpkin' is the definition.
(I've seen this in another clue)
'of a sort' is the wordplay.
'sort' indicates anagramming the letters.
'of'+'a'='ofa'
'ofa' with letters rearranged gives 'OAF'.
(Other definitions for oaf that I've seen before include "A clumsy or stupid person" , "An ill-mannered lout" , "Clumsy fool" , "Stupid or clumsy man" , "Boor or lout" .)