Savage cruelty (8)
I believe the answer is:
ferocity
'savage cruelty' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ferocity that I've seen before include "Savage cruelty of temperament" , "Cruel violence" , "Savagery, fierceness" , "Unrestrained and cruel savagery" , "Savageness" .)