Chance in card game initially blown (5)
I believe the answer is:
Here is my best explanation:
'chance' is the definition.
'card game initially blown' is the subsidiary indication.
'card game' becomes 'sevens' (sevens is a kind of card game).
'initially blown' means to remove the first letter.
'sevens' with its first letter taken off is 'evens'.
'in' is the link.
(Other definitions for evens that I've seen before include "50:50 probability", "Levels - odds", "These are odds, strangely", "Oddly, these could be odds", "In betting, winning the amount staked", "Smooths the odds", "Balanced odds", "Odds offering equal chance of win or lose", "Betting odds" and "Kind of betting odds on seven".)