Reversal
'reversal' is the definition.
(I know that reversal can be written as setback)
This is the entire clue.
(Other definitions for setback that I've seen before include "Check" , "Reversal of fortune" , "Problem" , "disappointment" , "Hitch" .)
(Other definitions for role that I've seen before include "Part, portrayal" , "Acting part" , "Part (in drama)" , "Part played (in life?)" , "Duty" .)