Weapons store unexpectedly ran sale (7)
I believe the answer is:
arsenal
'weapons store' is the definition.
(store for weapons or ammunition)
'unexpectedly ran sale' is the wordplay.
'unexpectedly' indicates an anagram.
'ran'+'sale'='ransale'
'ransale' with letters rearranged gives 'ARSENAL'.
(Other definitions for arsenal that I've seen before include "London premiership football team" , "6D 5A [TUBE STATION]" , "Where the guns are and who are The Gunners are" , "London football club - magazine" , "Weapon store - team" .)