Not safe (3)
I believe the answer is:
out
'not safe' is the definition.
('out' is the opposite to 'safe')
This is all the clue.
(Other definitions for out that I've seen before include "On strike - dismissed - unconsciousout" , "A way to escape" , "Not allowed - on strike" , "Heading back to the pavilion?" , "what batsman doesn't want to be" .)