In this practice there's a real share fluctuation (9)
I believe the answer is:
rehearsal
'in this practice' is the definition.
'rehearsal' can be an answer for 'practice' (rehearsal is a kind of practice). I'm not sure about the rest of the definition.
'there's a real share fluctuation' is the wordplay.
'there's' says to put letters next to each other.
'fluctuation' is an anagram indicator.
'real' next to 'share' is 'realshare'.
'realshare' anagrammed gives 'REHEARSAL'.
Can you help me to learn more?
(Other definitions for rehearsal that I've seen before include "Dummy run" , "Practice in theatre etc" , "show trial" , "Drill" , "Preparation for a show" .)