Champ's moment of truth (6)
I believe the answer is:
crunch
I believe this is a double definition.
'champ's' is the first definition.
(thesaurus)
'moment of truth' is the second definition.
(I've seen this before)
(Other definitions for crunch that I've seen before include "Process (lots of data)" , "Moment of truth" , "Crush noisily" , "Informally, a decisive event or showdown" , "Decisive moment" .)