To the cat turning tail, it's a gamble (4-2)
I believe the answer is:
toss-up
'a gamble' is the definition.
(thesaurus)
'to the cat turning tail' is the wordplay.
'the cat' becomes 'puss' (puss is a kind of cat).
'turning tail' is a reversal indicator.
'puss' written backwards gives 'ssup'.
'to'+'ssup'='TOSS-UP'
'it's' acts as a link.
(Other definitions for toss-up that I've seen before include "Flip of a coin" , "It helps you pick" , "Use of a coin to choose" , "Fifty-fifty chance" .)