Untidy state upset green courier (9)
I believe the answer is:
messenger
'courier' is the definition.
(I know that courier can be written as messenger)
'untidy state upset green' is the wordplay.
'untidy state' becomes 'mess' (state of being untidy).
'upset' indicates an anagram.
'green' anagrammed gives 'enger'.
'mess'+'enger'='MESSENGER'
(Other definitions for messenger that I've seen before include "Emissary, courier" , "Kind of bearer - don't shoot him" , "Courier - don't shoot him" , "Delivery boy" , "He's just bringing the word - don't shoot him" .)