Outwit champion concealing sudden move (6)
I believe the answer is:
twitch
'sudden move' is the definition.
(sudden twitch in the body)
'outwit champion concealing' is the wordplay.
'concealing' indicates a hidden word.
'TWITCH' is hidden in the letters of 'outwit champion'.
(Other definitions for twitch that I've seen before include "Move spasmodically" , "Uncontrolled, jerky motion" , "jump" , "Quiver or jerk spasmodically" , "Make a convulsive movement" .)