Scout, hence improvised shield (10)
I believe the answer is:
escutcheon
'shield' is the definition.
(escutcheon is a kind of shield)
'scout hence improvised' is the wordplay.
'improvised' indicates an anagram (I've seen this in other clues).
'scout'+'hence'='scouthence'
'scouthence' is an anagram of 'ESCUTCHEON'.
(Other definitions for escutcheon that I've seen before include "Heraldic emblem" , "Heraldic shield" , "Family shield" .)