Stone thrown in attack (3,2)
I believe the answer is:
set on
'attack' is the definition.
('set on' can be a synonym of 'attack')
'stone thrown' is the wordplay.
'thrown' indicates an anagram.
'stone' with letters rearranged gives 'SET ON'.
'in' is the link.
(Other definitions for set on that I've seen before include "Go" , "Determined" , "Attack" .)