Failure to notice supervision (9)
I believe the answer is:
oversight
I believe this clue is a double definition.
'failure to notice' is the first definition.
(I've seen this before)
'supervision' is the second definition.
('oversight' can be a synonym of 'supervision')
(Other definitions for oversight that I've seen before include "act of negligence" , "Supervision - omission" , "Failure to notice something" , "Lapse" , "A failure to notice, an omission" .)