Pieces of land used for races (5)
I believe the answer is:
acres
'pieces' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how they can define each other.
'land used for races' is the wordplay.
'land' becomes 'acre' (I've seen this before).
'used for races' becomes 's' (I can't explain this - if you can you should believe this answer much more).
'acre'+'s'='ACRES'
'of' is the link.
Can you help me to learn more?
(Other definitions for acres that I've seen before include "Scare (anag)" , "may burden landed folk" , "Cares about the tracts of land" , "Cares about the land measures" , "Extensive landed property (often rolling)" .)