After theatre, even in coma playing instrument (9)
I believe the answer is:
harmonica
'instrument' is the definition.
(harmonica is a kind of instrument)
'after theatre even in coma playing' is the wordplay.
'after' is a charade indicator (letters next to each other).
'even' indicates alternate letters (even-numbered letters are used).
'playing' indicates anagramming the letters.
The alternating letters of 'theatre' are 'har'.
'in'+'coma'='incoma'
'incoma' is an anagram of 'monica'.
'har'+'monica' is 'HARMONICA'.
(Other definitions for harmonica that I've seen before include "It's played by blowing into holes" , "Blow me!" , "glasses of water" , "Larry Adler's instrument" , "An alternative mouth-organ" .)