Catches held in genuine practice session (9)
I believe the answer is:
rehearsal
'practice session' is the definition.
(rehearsal is a kind of practice session)
'catches held in genuine' is the wordplay.
'catches' becomes 'hears' (I've seen this in another clue).
'held in' means one lot of letters goes inside another.
'genuine' becomes 'real' (similar in meaning).
'hears' inserted into 'real' is 'REHEARSAL'.
(Other definitions for rehearsal that I've seen before include "Drill" , "Dry run" , "show trial" , "Practice in theatre etc" , "Play run-through" .)