It shows you're wrong on both scores - and cheat (6-5)
I believe the answer is:
double-cross
'cheat' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for double-cross that I've seen before include "Cheat - betray" , "Betray - XX?" , "Deceive person one is supposedly helping" , "Deceive supposed ally" , "Deceive, betray" .)