Light altercation about sack (3,4,2)
I believe the answer is:
set fire to
'light' is the definition.
(thesaurus)
'altercation about sack' is the wordplay.
'altercation' becomes 'setto' (I've seen this before).
'about' indicates putting letters inside.
'sack' becomes 'fire' ('fire' can be a synonym of 'sack'**).
'setto' placed around 'fire' is 'SET FIRE TO'.
(Other definitions for set fire to that I've seen before include "Light" , "Ignite" , "torch" .)