Not entirely secure as top bridge-player (4)
I believe the answer is:
east
'bridge-player' is the definition.
(I've seen this before)
'not entirely secure as top' is the wordplay.
'not entirely' says the answer is hidden in the clue.
'EAST' is hidden within 'secure as top'.
(Other definitions for east that I've seen before include "On most maps it's right!" , "Ninety degree bearing" , "One of four at table" , "Direction of the rising sun" , "major point" .)