Alternative point roughly behind duck (6)
I believe the answer is:
option
'alternative' is the definition.
('option' can be a synonym of 'alternative')
'point roughly behind duck' is the wordplay.
'roughly' indicates anagramming the letters.
'behind' says to put letters next to each other.
'duck' becomes 'o'.
'point' with letters rearranged gives 'ption'.
'ption' after 'o' is 'OPTION'.
(Other definitions for option that I've seen before include "Freedom to choose" , "possibility" , "Possible choice" , "Choice of portion" , "Alternative for choice" .)