That woman's lad upset messenger (6)
I believe the answer is:
herald
'messenger' is the definition.
(I know that herald is a type of messenger)
'that woman's lad upset' is the wordplay.
'that woman' becomes 'her' ('her' refers to a woman).
'upset' is an anagram indicator.
'lad' with letters rearranged gives 'ald'.
'her'+'ald'='HERALD'
(Other definitions for herald that I've seen before include "College of Arms official" , "Person who announces important news" , "One making proclamations - harbinger" , "Signal the arrival of" , "Harbinger, messenger" .)