Group to fight (3-2)
I believe the answer is:
set-to
'fight' is the definition.
(I know that set-to is a type of fight)
'group to' is the wordplay.
'group' becomes 'set' (both can mean a collection).
'set'+'to'='SET-TO'
(Other definitions for set-to that I've seen before include "Scrap" , "Ready - fight" , "Altercation" , "Brief fight" , "brush with violence?" .)