Left in pieces after contestant finally made a mistake (7,2)
I believe the answer is:
tripped up
'made a mistake' is the definition.
(tripping up is a kind of making a mistake)
'left in pieces after contestant finally' is the wordplay.
'left in pieces' becomes 'ripped up' (torn into pieces).
'after' is a charade indicator (letters next to each other).
'finally' says to take the final letters.
The final letter of 'contestant' is 't'.
'rippedup' put after 't' is 'TRIPPED UP'.
(Other definitions for tripped up that I've seen before include "stumbled" , "Came a cropper" , "Made a mistake" .)