Mislaying or failing to win (6)
I believe the answer is:
losing
I believe this is a double definition.
'mislaying' is the first definition.
('lose' can be a synonym of 'mislay')
'failing to win' is the second definition.
('lose' can be a synonym of 'fail to win')
(Other definitions for losing that I've seen before include "being beaten?" , "Mislaying or being defeated" , "Confusing" , "Mislaying; failing to win" , "Failing to keep" .)