Oddball in Rio wed in disguise (6)
I believe the answer is:
weirdo
'oddball' is the definition.
(thesaurus)
'rio wed in disguise' is the wordplay.
'in disguise' indicates an anagram.
'rio'+'wed'='riowed'
'riowed' with letters rearranged gives 'WEIRDO'.
'in' is the link.
(Other definitions for weirdo that I've seen before include "Freak" , "Person who behaves bizarrely" , "Eccentric type" , "Odd type" , "Bizarre character" .)