Managed by mistake to ignore two leaders (5)
I believe the answer is:
under
'managed by' is the definition.
(as in working 'under' a supervisor or manager)
I don't understand how the remainder of the clue works.
(Other definitions for under that I've seen before include "Subject to the authority of" , "Beneath or subordinate to" , "In a state of unconsciousness" , "Managed by" , "Sub" .)