In a race, perhaps not the whole field (4)
I believe the answer is:
acre
'field' is the definition.
(I've seen this in another clue)
'in a race perhaps not the whole' is the wordplay.
'race' can be anagrammed to 'ACRE'.
Though, I'm unsure how this is indicated.
Can you help me to learn more?
(Other definitions for acre that I've seen before include "marine location in Israel" , "0.405 of a hectare" , "Race (anag.)" , "stretch of land" , "Area measure - Israeli port - Brazilian state" .)