Racing one out of foolishness (9)
I believe the answer is:
ignorance
'foolishness' is the definition.
(thesaurus)
'racing one out' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'racing'+'one'='racingone'
'racingone' anagrammed gives 'IGNORANCE'.
'of' acts as a link.
(Other definitions for ignorance that I've seen before include "Lack of knowledge" , "being uninformed" , "Stupidity" , "'Where . . . . . . . . . is bliss, 'tis folly to be wise'" , "Being in the dark" .)