Cowards' sad return to darts organisation (8)
I believe the answer is:
dastards
'cowards'' is the definition.
(dastard is a kind of coward)
'sad return to darts organisation' is the wordplay.
'return' is a reversal indicator.
'to' is a charade indicator (letters next to each other).
'organisation' is an anagram indicator.
'sad' reversed gives 'das'.
'darts' with letters rearranged gives 'tards'.
'das'+'tards'='DASTARDS'
(Other definitions for dastards that I've seen before include "Cowards" , "scoundrels" .)