Becomes aware that this will interrupt the actual run-through (9)
I believe the answer is:
rehearsal
'run-through' is the definition.
(I know that run-through can be written as rehearsal)
'becomes aware that this will interrupt the actual' is the wordplay.
'becomes aware' becomes 'hears' (I can't justify this - if you can you should believe this answer much more).
'that this will interrupt' is an insertion indicator.
'the actual' becomes 'real' (I've seen this in another clue).
'hears' inserted within 'real' is 'REHEARSAL'.
Can you help me to learn more?
(Other definitions for rehearsal that I've seen before include "Practice session in preparation for public performance" , "Play run-through" , "Practice in theatre etc" , "preparation in house?" , "show trial" .)