Unkind words earned a bad mark (5)
I believe the answer is:
smear
This could be a double definition.
'unkind words' is the first definition.
(misinformation spread about someone)
'a bad mark' is the second definition.
'earned' is the link.
This may not be right. It may belong to one of the definitions.
(Other definitions for smear that I've seen before include "Spread dirty substance, try to damage reputation" , "Greasy or sticky mark" , "Sully" , "Unwarranted accusation" , "False report" .)