Overdraft in wobbly organisation's a setback (4,4)
I believe the answer is:
body blow
'a setback' is the definition.
(I have seen 'Serious setback' mean 'body blow' so perhaps 'setback' could also mean 'body blow')
'overdraft in wobbly organisation's' is the wordplay.
'overdraft' becomes 'od'.
'in' is an insertion indicator.
'organisation' is an anagram indicator.
'wobbly' is an anagram of 'byblow'.
'od' placed inside 'byblow' is 'BODY BLOW'.
(Other definitions for body blow that I've seen before include "Crushing reverse" , "Severe disappointment" , "A severe setback, like punch to solar plexus" , "Sickening reverse" , "Huge setback" .)