Reveal secret to let opposition win (4,3,4,4)
I believe the answer is:
give the game away
'reveal secret' is the definition.
(to give the game away is to reveal a secret)
I cannot understand how the rest of the clue works.
(Other definitions for give the game away that I've seen before include "Get rid of the bag" , "dispose of bag for nothing" , "show one's hand" , "resign?" , "Let cat out of bag" .)