Article changing entire racecourse (7)
I believe the answer is:
aintree
'racecourse' is the definition.
(horseracing venue in Liverpool)
'article changing entire' is the wordplay.
'article' becomes 'a' (English indefinite article).
'changing' indicates anagramming the letters.
'entire' is an anagram of 'intree'.
'a'+'intree'='AINTREE'
(Other definitions for aintree that I've seen before include "Liverpool's racecourse" , "Venue of the Grand National race" , "National racecourse" , "Here they run" , "Merseyside racecourse" .)