Take part in game with extremely eager theatre attender (8)
I believe the answer is:
'theatre attender' is the definition.
(I've seen this before)
'take part in game with extremely eager' is the wordplay.
'take part in' becomes 'play' (I can't explain this - if you can you should give a lot more credence to this answer).
'game' becomes 'go game' (go is a board game).
'with' says to put letters next to each other.
'extremely' suggests removing the centre (only the extremes of the word are used).
'eager' with its middle removed is 'er'.
Can you help me to learn more?
(Other definitions for playgoer that I've seen before include "He likes the Theatre" , "one the gods may accommodate" , "who likes a bit of drama?" , "One who's regularly seen in theatre" , "Person in theatre" .)