Where you'll see races keep so many gathering (5)
I believe the answer is:
epsom
'where you'll see races' is the definition.
(Epsom racecourse)
'keep so many gathering' is the wordplay.
'gathering' says the answer is hidden in the clue (parts of the clue hold or gather the answer).
'EPSOM' is hidden in the letters of 'keep so many'.
(Other definitions for epsom that I've seen before include "place for racing" , "Mopes around in English horse-racing venue" , "& 5 Purgative medicine" , "Surrey race course" , "can have horses" .)