Make a mistake in bumper race (3)
I believe the answer is:
err
'make a mistake' is the definition.
(I've seen this before)
'in bumper race' is the wordplay.
'in' says the answer is hidden in the clue.
'ERR' can be found hidden inside 'bumper race'.
(Other definitions for err that I've seen before include "Make mistakes" , "Bungle" , "Go wrong" , "Be incorrect" , "'to... is human,to forgive divine'" .)