Champ in moment of truth? (6)
I believe the answer is:
crunch
I believe this clue is a double definition.
'champ' is the first definition.
(thesaurus)
'moment of truth?' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for crunch that I've seen before include "Informally, a decisive event or showdown" , "Crush noisily" , "Bite noisily - moment of decision" , "Chew something hard" , "Decisive moment" .)