What's the betting contracted game won't start? (5)
I believe the answer is:
evens
'what's the betting' is the definition.
(type of betting odds)
'contracted game won't start?' is the wordplay.
'contracted game' becomes 'sevens' (short for rugby sevens).
'won't start?' means to remove the first letter.
'sevens' with its first letter removed is 'EVENS'.
(Other definitions for evens that I've seen before include "Balanced odds" , "Kind of betting odds on seven" , "50:50 probability" , "Fifty-fifty odds" , "Levels - odds" .)