Area of land used for the race, possibly (7)
I believe the answer is:
hectare
'area of land' is the definition.
(hectare is a unit for measuring land area)
'the race possibly' is the wordplay.
'possibly' indicates anagramming the letters.
'the'+'race'='therace'
'therace' anagrammed gives 'HECTARE'.
'used for' acts as a link.
(Other definitions for hectare that I've seen before include "Metric unit of area" , "Teacher of metric land measure" , "10,000 squaer metres" , "10,000 square metres" , "Some land in France" .)