Great love reformed despicable chap (6)
I believe the answer is:
toerag
'despicable chap' is the definition.
(I've seen this before)
'great love reformed' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'reformed' indicates an anagram.
'great'+'o'='greato'
'greato' with letters rearranged gives 'TOERAG'.
(Other definitions for toerag that I've seen before include "despicable sort" , "Despicable chap" , "contemptible sort" , "Despicable character" , "Despicable person (slang)" .)