Scout, hence improvised shield (10)
I believe the answer is:
'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).
'scouthence' is an anagram of 'ESCUTCHEON'.
(Other definitions for escutcheon that I've seen before include "Heraldic emblem" , "Heraldic shield" , "Family shield" .)