Overlooked soldier set up a sort of drone (7)
I believe the answer is:
ignored
'overlooked' is the definition.
(I've seen this before)
'soldier set up a sort of drone' is the wordplay.
'soldier' becomes 'GI' (term for US soldier).
'set up' is a reversal indicator (in a down clue, letters go up).
'a sort of' is an anagram indicator.
'gi' backwards is 'ig'.
'drone' with letters rearranged gives 'nored'.
'ig'+'nored'='IGNORED'
(Other definitions for ignored that I've seen before include "Left out in the cold" , "Turned a blind eye to" , "overlooked" , "Failed to notice" , "Neglected" .)