If possibly communist, shot! (5)
I believe the answer is:
fired
'shot' is the definition.
(firing is a kind of shooting)
'if possibly communist' is the wordplay.
'possibly' is an anagram indicator.
'communist' becomes 'red' (red can informally mean communist).
'if' is an anagram of 'fi'.
'fi'+'red'='FIRED'
(Other definitions for fired that I've seen before include "Aroused" , "(Of pottery) baked" , "Dismissed or ignited" , "Sacked or ignited" , "Set ablaze" .)