Immoral and corrupt umpire (6)
I believe the answer is:
impure
'immoral' is the definition.
(thesaurus)
'corrupt umpire' is the wordplay.
'corrupt' indicates an anagram.
'umpire' anagrammed gives 'IMPURE'.
'and' is the link.
(Other definitions for impure that I've seen before include "Unclean" , "Sullied or adulterated" , "Adulterated or unchaste" , "Defiled" , "Tainted, not chaste" .)