Left a group working with editor (9)
I believe the answer is:
abandoned
'left' is the definition.
(abandoning is a kind of leaving)
'a group working with editor' is the wordplay.
'group' becomes 'band' (band is a kind of group**).
'working' becomes 'on'.
'with' is a charade indicator (letters next to each other).
'editor' becomes 'ed'.
'a'+'band'+'on'+'ed'='ABANDONED'
(Other definitions for abandoned that I've seen before include "Left - dissolute" , "Derelict, deserted" , "No longer inhabited and left desolate" , "Forsook, left behind" , "Quit" .)