English novelist’s editor backed rival (5)
I believe the answer is:
defoe
'english novelist's' is the definition.
(I've seen this before)
'editor backed rival' is the wordplay.
'editor' becomes 'ed'.
'backed' is a reversal indicator.
'rival' becomes 'foe' (foe is a kind of rival).
'ed' back-to-front is 'de'.
'de'+'foe'='DEFOE'
(Other definitions for defoe that I've seen before include "See 14" , "Daniel . . . . . wrote ''Robinson Crusoe'' (5)" , "Robinson Crusoe's creator, d. 1731" , "Daniel -, Moll Flanders author" , "Daniel ---, wrote Moll Flanders" .)