Race; hat (5)
I believe the answer is:
derby
This clue is a double definition.
'race' is the first definition.
(I've seen this before)
'hat' is the second definition.
(derby is a kind of hat)
(Other definitions for derby that I've seen before include "Cathedral city on the River Derwent" , "Epsom horse race" , "Gracefully thin" , "Local game" , "Classic horse-race" .)