Smart refusal to be out of the race (5)
I believe the answer is:
natty
'smart' is the definition.
(I've seen this in another clue)
'refusal to be out of the race' is the wordplay.
'refusal' becomes 'nay' (I've seen this in another clue).
'to be out of' means one lot of letters goes inside another.
'the race' becomes 'tt'.
'nay' enclosing 'tt' is 'NATTY'.
(Other definitions for natty that I've seen before include "Smart, fashionable (colloq.)" , "Stylish" , "Dapper (colloq.)" , "Informally neat and well-dressed" , "Smart, spruce" .)