Cruel person using this force (5)
I believe the answer is:
brute
I believe this is a double definition.
'cruel person' is the first definition.
(I've seen this before)
'this force' is the second definition.
(thesaurus)
'using' acts as a link.
(Other definitions for brute that I've seen before include "Cruelly rapacious person" , "One monstrous" , "Monster" , "Cruel person" , "Heartless individual" .)