Not a true origin of race perhaps (5,5)
I believe the answer is:
false start
'not a true' is the definition.
I know nothing about this answer so I can't judge whether this works.
'origin of race perhaps' is the wordplay.
I cannot quite see how this works, but
'origin' could be 'start' (I've seen this in another clue) and 'start' is present in the answer.
The remaining letters 'false' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for false start that I've seen before include "may lead to total recall" , "In which runner is seen to have jumped the gun" , "Unsuccessful beginning" , "In which someone jumps the gun" .)