Be there in this (10)
I believe the answer is:
attendance
'be there in this' is the definition.
(if you are in attendance you are there)
'be there in this' is the wordplay.
'be there' becomes 'attend' (I've seen this before).
'in this' becomes 'ance' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'attend'+'ance'='ATTENDANCE'
Can you help me to learn more?
(Other definitions for attendance that I've seen before include "Number present" , "Presence; gate" , "all that turned up" , "Act of being present" , "Number at gathering" .)