Make a mistake in bumper race (3)
I believe the answer is:
Here is my best explanation:
'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 "Go wrong", "Stray from the straight and narrow", "Drop a clanger", "Miss the mark", "'to... is human,to forgive divine'", "Do wrong", "blunder", "Slip up", "Transgress" and "Deviate".)