At sea, a duck coming in low (6)
I believe the answer is:
afloat
'at sea' is the definition.
(similar in meaning)
'a duck coming in low' is the wordplay.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'coming in' is an insertion indicator.
'low' becomes 'flat' (I've seen this before).
'o' put inside 'flat' is 'float'.
'a'+'float'='AFLOAT'
(Other definitions for afloat that I've seen before include "On board a ship or boat" , "At sea, on the water" , "Buoyant: solvent" , "Out of debt; at sea" , "On board a ship; out of difficulty" .)