Group support for an unfortunate event (7)
I believe the answer is:
setback
'an unfortunate event' is the definition.
(I've seen this before)
'group support' is the wordplay.
'group' becomes 'set' (both can mean a collection).
'support' becomes 'back' (to back is to support or endorse).
'set'+'back'='SETBACK'
'for' acts as a link.
(Other definitions for setback that I've seen before include "Reverse" , "Snag" , "Hindrance to progress" , "Reversal of fortune" , "unfortunate event" .)