Sack one likely to get fired (5)
I believe the answer is:
rifle
I believe this clue is a double definition.
'sack' is the first definition.
(both can mean to steal)
'one likely to get fired' is the second definition.
(a rifle can be fired)
(Other definitions for rifle that I've seen before include "An arm" , "Gun with a long barrel" , "Weapon - sack" , "Long-barrelled weapon, normal army equipment" , "shoot?" .)