Commenced attack (3,5)
I believe the answer is:
set about
I believe this clue is a double definition.
'commenced' is the first definition.
(I've seen this in another clue)
'attack' is the second definition.
(I know that attack is a more specific form of the action set about)
(Other definitions for set about that I've seen before include "Start to do something with determination" , "Get cracking" , "Embark upon" , "Begin - attack" .)