Defame African country no good after revolution (6)
I believe the answer is:
malign
'defame' is the definition.
(maligning is a kind of defaming)
'african country no good after revolution' is the wordplay.
'african country' becomes 'mali' (Mali is an example).
'no' becomes 'n' (common abbreviation).
'good' becomes 'g' (abbreviation).
'after revolution' says the letters should be written backwards.
'n'+'g'='ng'
'ng' back-to-front is 'gn'.
'mali'+'gn'='MALIGN'
(Other definitions for malign that I've seen before include "Of ill intent" , "run down" , "Wicked, evil" , "Say unpleasant and untrue things about" , "Traduce" .)