Gone bad (6)
(Other definitions for sour that I've seen before include "Turned - morose" , "Bitter, tart" , "Moody - acid" , "Acid, tart" , "Acid or caustic" .)
'gone bad' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for spoilt that I've seen before include "Marred" , "Overindulged" , "messed up" , "Harmed" , "Deprived" .)
This clue is a double definition.
'gone' is the first definition.
(as in going off somewhere)
'bad?' is the second definition.
(eg meat that's gone off is bad)
(Other definitions for off that I've seen before include "No longer available" , "Turned, sour" , "Fielding side" , "below par" , "Complete (6,3) - See 14" .)