Just what you’d expect of an actor when performing (2,9)
I believe the answer is:
'just what you'd expect' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'an actor when performing' is the wordplay.
'an actor when' becomes 'in' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'performing' becomes 'character' (character is a kind of performing).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for in character that I've seen before include "Typical" , "True to type" , "Appropriate for the part" , "Dressed for the part" .)