Josh is realistic before prank (9,4)
I believe the answer is:
practical joke
'prank' is the definition.
(practical joke is a kind of prank)
'josh is realistic before' is the wordplay.
'josh' becomes 'joke' (I can't explain this - if you can you should believe this answer much more).
'is realistic' becomes 'practical' (similar in meaning).
'before' says to put letters next to each other.
'joke' put after 'practical' is 'PRACTICAL JOKE'.
Can you help me to learn more?
(Other definitions for practical joke that I've seen before include "rag" , "Trick played to discomfort someone" , "Prank designed to make a fool of its victim" , "Unkind prank" , "Jape - hoax" .)