Contestant’s appearance ignoring a rule (5)
I believe the answer is:
rival
'contestant's' is the definition.
(rival is a kind of contestant)
I can't explain the rest of the clue.
(Other definitions for rival that I've seen before include "Adversary or foe" , "Emulate" , "Adversary, antagonist" , "Competitor; be as good as" , "Be equal to in quality" .)