Establish a race isn't fixed (9)
I believe the answer is:
ascertain
'establish' is the definition.
(I've seen this before)
'a race isn't fixed' is the wordplay.
'fixed' indicates an anagram.
'race'+'isnt'='raceisnt'
'raceisnt' with letters rearranged gives 'scertain'.
'a'+'scertain'='ASCERTAIN'
(Other definitions for ascertain that I've seen before include "Verify" , "Get to know" , "Find out by making enquiries in sectarian way" , "Establish after an investigation or study" , "Cartesian (anag)" .)