Dominion loses leader, who is replaced by upstart referee (6)
I believe the answer is:
umpire
This might be a double definition.
'dominion loses leader who is replaced by upstart' is the first definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'referee' is the second definition.
(synonyms)
Can you help me to learn more?
(Other definitions for umpire that I've seen before include "Impartial supervisor" , "The ref in cricket match" , "Official at a cricket match" , "Impure (anag) - adjudicator" , "Arbiter of cricket match" .)