Incentive to turn up during motor racing (6)
I believe the answer is:
carrot
'incentive' is the definition.
(as in a carrot and stick)
'turn up during motor racing' is the wordplay.
'turn up' says the letters should be written backwards.
'during' indicates the answer is hidden within the clue.
'torrac' is hidden in the letters of 'motor racing'.
'torrac' in reverse letter order is 'CARROT'.
'to' acts as a link.
(Other definitions for carrot that I've seen before include "Orange edible root" , "Vegetable to entice the donkey" , "Rewarding vegetable?" , "Tapering vegetable" , "Root vegetable" .)