At heart, Simon is confused about play in Dublin theatre (7)
I believe the answer is:
olympia
'dublin theatre' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for olympia that I've seen before include "Chief sanctuary of Zeus" , "traditional home of games" , "Capital of Washington state, and site of ancient Games" , "plain in Greece" , "Greek district" .)