Deliberate cruelty (6)
I believe the answer is:
sadism
'deliberate cruelty' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for sadism that I've seen before include "Delight taken in cruelty" , "Taking pleasure in inflicting pain" , "Cruel behaviour" , "The love of cruelty" , "Deviancy" .)