Challenger bogus, by the sound of it? (3)
I believe the answer is:
foe
'challenger' is the definition.
(foe is a kind of challenger)
'bogus by the sound of it?' is the wordplay.
'bogus' becomes 'faux' (faux means fake).
'by the sound of it?' indicates a 'sounds like' (homophone) clue.
'faux' is a homophone of 'FOE'.
(Other definitions for foe that I've seen before include "Antagonist" , "Opposition" , "opposing side" , "Evil rival" , "Opponent" .)