Victor is a little treacherous (4)
I believe the answer is:
hero
'victor' is the definition.
(both can mean a champion)
'a little treacherous' is the wordplay.
'a little' indicates a hidden word.
'HERO' is hidden in the letters of 'treacherous'.
'is' acts as a link.
(Other definitions for hero that I've seen before include "Chief good guy in a book or film" , "Principal character in a film or novel" , "Leander's lover, who committed suicide when he drowned" , "Chief good guy in a story" , "Principal boy" .)