... celebrity champion shows formality (6)
I believe the answer is:
starch
'formality' is the definition.
(I've seen this before)
'celebrity champion' is the wordplay.
'celebrity' becomes 'star' (I've seen this before).
'champion' becomes 'ch' (I've seen this in other clues).
'star'+'ch'='STARCH'
'shows' is the link.
(Other definitions for starch that I've seen before include "ceremony" , "Carbohydrate that occurs in all green plants" , "Stiffener in the laundry" , "Stiffening agent" , "rigid" .)