Person upset by sad and severe setback (4,4)
I believe the answer is:
body blow
'severe setback' is the definition.
(I've seen this before)
'person upset by sad' is the wordplay.
'person' becomes 'bod' (I've seen this in other clues).
'upset' is a reversal indicator.
'sad' becomes 'low' (I am not sure about this - if you are sure you should believe this answer much more).
'by' back-to-front is 'yb'.
'bod'+'yb'+'low'='BODY BLOW'
'and' is the link.
Can you help me to learn more?
(Other definitions for body blow that I've seen before include "A severe setback, like punch to solar plexus" , "Severe disappointment" , "Huge setback" , "Sickening reverse" , "Severe setback, like thump to torso" .)