District Attorney: I vet awkward case (6)
I believe the answer is:
dative
'case' is the definition.
(dative is a kind of case)
'district attorney i vet awkward' is the wordplay.
'district attorney' becomes 'da' ('D.A.' can be a synonym of 'district attorney').
'awkward' indicates anagramming the letters.
'i'+'vet'='ivet'
'ivet' is an anagram of 'tive'.
'da'+'tive'='DATIVE'
(Other definitions for dative that I've seen before include "Grammatical case" , "'To' case (grammar)" .)