Author given poor grades by enemy? (5)
I believe the answer is:
defoe
'author' is the definition.
(Daniel Defoe)
'poor grades by enemy?' is the wordplay.
'poor grades' becomes 'de' (I've seen this in other clues).
'by' means one lot of letters go next to another.
'enemy?' becomes 'foe' (foe can mean an enemy or rival).
'de'+'foe'='DEFOE'
'given' acts as a link.
(Other definitions for defoe that I've seen before include "Daniel --, English novelist" , "Daniel, writer, d. 1731" , "Writer of Moll Flanders" , "Daniel -, Moll Flanders author" , "Daniel ---, wrote Moll Flanders" .)