Ducks spotted in vacant land? It's unexplained (5,3)
I believe the answer is:
loose end
'it's unexplained' is the definition.
(something still to be resolved or explained)
'ducks spotted in vacant land?' is the wordplay.
'ducks' becomes 'OO' (duck means zero in cricket).
'spotted' becomes 'seen' (spot can mean to see or notice).
'in' is an insertion indicator.
'vacant land?' becomes 'ld' (I can't explain this - if you can you should believe this answer much more).
'oo'+'seen'='ooseen'
'ooseen' going within 'ld' is 'LOOSE END'.
(Other definitions for loose end that I've seen before include "where one's idling" , "Unsettled matter" , "should have been tied?" , "Detail not yet settled" , "One's not yet decided" .)