Cowards’ sad return to darts organisation (8)
I believe the answer is:
Here is my best explanation:
'cowards' is the definition.
(dastard is a kind of coward)
'sad return to darts organisation' is the subsidiary indication.
'return' says the letters should be written backwards.
'organisation' is an anagram indicator.
'sad' back-to-front is 'das'.
'darts' anagrammed gives 'tards'.
(Other definitions for dastards that I've seen before include "Cowards" and "scoundrels".)