Maybe crude part in hissy fit? I'm not sure (9)
I believe the answer is:
petroleum
'maybe crude' is the definition.
(crude oil is a petroleum product)
'part in hissy fit? i'm not sure' is the wordplay.
'part' becomes 'role' (synonyms).
'in' means one lot of letters goes inside another.
'hissy fit?' becomes 'pet' (I can't explain this - if you can you should believe this answer much more).
'i'm not sure' becomes 'um' (expression of hesitation).
'pet'+'um'='petum'
'role' placed within 'petum' is 'PETROLEUM'.
(Other definitions for petroleum that I've seen before include "Source of fuel" , "Crude oil" , "Oil well product" , "Hydrocarbon oil" , "Fossil fuel" .)