Main drawback away from land (7)
I believe the answer is:
seaward
'away from land' is the definition.
(I've seen this in another clue)
'main drawback' is the wordplay.
'main' becomes 'sea' (the main is an old name for the sea).
'drawback' becomes 'ward' (I've seen this in other clues).
'sea'+'ward'='SEAWARD'
(Other definitions for seaward that I've seen before include "Towards the ocean" , "heading for coast?" , "Like sailor going out" .)