Surely not turning back on fortune? (2,6)
I believe the answer is:
no chance
'surely not' is the definition.
(phrase used to show you think something unlikely)
'turning back on fortune?' is the wordplay.
'turning back' says the letters should be written backwards.
'fortune?' becomes 'chance' (synonyms).
'on' in reverse letter order is 'no'.
'no'+'chance'='NO CHANCE'
(Other definitions for no chance that I've seen before include "pessimistic forecast" , "Most unlikely!" , "That will not happen/succeed" , "Monopoly could be badly affected by this" , "That's definitely out" .)