Biased big shot at Lord's returns in group (6)
I believe the answer is:
sexist
'biased' is the definition.
(thesaurus)
'big shot at lord's returns in group' is the wordplay.
'big shot at lord's' becomes 'six' (six runs in cricket - Lord's is a cricket ground).
'returns' says the letters should be written in reverse.
'in' is an insertion indicator.
'group' becomes 'set' (both can mean a collection).
'six' reversed gives 'xis'.
'xis' going into 'set' is 'SEXIST'.
(Other definitions for sexist that I've seen before include "Prejudiced on grounds of gender" , "Exists (anag.)" , "discriminating against women?" , "Bigot" , "Discriminatory on the basis of gender" .)