Ethnic groups in competitions (5)
I believe the answer is:
races
I believe this clue is a double definition.
'ethnic groups' is the first definition.
(I've seen this before)
'competitions' is the second definition.
(race is a kind of competition)
'in' is the link.
(Other definitions for races that I've seen before include "Moves very fast" , "Operates at excessive speed" , "Competitive trials of speed" , "Events at Epsom or Ascot?" , "Rushes" .)