Apply badly or incorrectly (6)
I believe the answer is:
misuse
'apply badly or incorrectly' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for misuse that I've seen before include "bad treatment" , "bad practice" , "Treat the wrong way or for the wrong purpose" , "Improper application" , "Apply badly or incorrectly" .)