Get better at racing event (5)
I believe the answer is:
rally
This clue is a double definition.
'get better' is the first definition.
(I've seen this before)
'racing event' is the second definition.
'at' is the link.
(Other definitions for rally that I've seen before include "Regain one's strength" , "Regain health" , "Arouse for action" , "Large gathering" , "Recover strength after illness" .)