Crossword Genius

Fifty per cent chance of drunk returning drink (4-2)

Ross

I believe the answer is:

toss-up

I'm a little stuck... Click here to teach me more about this clue!

'fifty per cent chance' is the definition.
I can't judge whether this definition defines the answer.

'drunk returning drink' is the wordplay.
'drunk' becomes 'sot' ('sot' can be a synonym of 'drunk').
'returning' says the letters should be written backwards.
'drink' becomes 'sup' (I've seen this before).
'sot' written backwards gives 'tos'.
'tos'+'sup'='TOSS-UP'

'of' acts as a link.

Can you help me to learn more?

(Other definitions for toss-up that I've seen before include "Flip of a coin" , "Fifty-fifty chance" , "It helps you pick" , "Use of a coin to choose" .)

I've seen this clue in The Telegraph.
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