Theatre player guarding the entrance (10)
I believe the answer is:
gatekeeper
'theatre player' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe there's a link between them I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for gatekeeper that I've seen before include "Entry attendant; butterfly" , "man at wicket" , "Entrance attendant" .)