Joined squad with hack (6)
I believe the answer is:
united
'joined' is the definition.
(uniting is a kind of joining)
'squad with hack' is the wordplay.
'squad' becomes 'unit' (both can mean a group of soldiers).
'with' says to put letters next to each other.
'hack' becomes 'ed' (hack can mean journalist, ed short for editor).
'unit'+'ed'='UNITED'
(Other definitions for united that I've seen before include "Brought or joined together" , "Agreed" , "Joined into a single entity" , "... we stand, divided we fall" , "See 14" .)