Darren failing in task (6)
I believe the answer is:
errand
'task' is the definition.
(an errand is a task or job)
'darren failing' is the wordplay.
'failing' indicates anagramming the letters (a failed spelling of the word).
'darren' with letters rearranged gives 'ERRAND'.
'in' is the link.
(Other definitions for errand that I've seen before include "Short assignment" , "Native of a former German kingdom" , "Short journey to get or carry message" , "A short journey to deliver orget goods" , "Trip for small task" .)