Chew noisily (6)
(Other definitions for crunch that I've seen before include "Decisive moment" , "Moment of truth" , "Informally, a decisive event or showdown" , "Crush noisily" , "Chew something hard" .)
(Other definitions for chomp that I've seen before include "Chew" , "For crunch" , "Munch noisily (colloq.)" .)
'chew noisily' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for munch that I've seen before include "Eat audibly; painter" , "Chew; Norwegian artist" , "who put one screaming on the canvas?" , "Norwegian painter" , "Edvard -, Norwegian artist (The Scream)" .)