Soldiers Mary shot (4)
I believe the answer is:
army
'soldiers' is the definition.
(group of soldiers)
'mary shot' is the wordplay.
'shot' indicates an anagram.
'mary' is an anagram of 'ARMY'.
(Other definitions for army that I've seen before include "Body of people organised for war" , "See 21" , "Fighting unit" , "Horde" , "Vast number" .)