Some land a sort of race (4)
I believe the answer is:
acre
'some land' is the definition.
(unit of land)
'a sort of race' is the wordplay.
'a sort of' indicates an anagram.
'race' is an anagram of 'ACRE'.
(Other definitions for acre that I've seen before include "point four nought five of a hectare" , "Unit of land area" , "Unit of land measurement" , "Measure of land area" , "Imperial land measure" .)