Amount of land set out for the race (7)
I believe the answer is:
hectare
'amount' is the definition.
(hectare is a kind of amount)
'land set out for the race' is the wordplay.
'the race' anagrams to 'HECTARE'.
However, I'm not sure how the anagram is indicated.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for hectare that I've seen before include "Surface area equal to 10,000 square meters" , "Metric measure of area" , "Extent" , "Metric land area" , "10,000 square metres" .)