Coin toss (4)
I believe the answer is:
flip
'coin toss' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for flip that I've seen before include "Toss - impertinent" , "Toss or flick in the air" , "Throw a wobbly" , "B-side" , "Turn quickly over; sort of chart" .)