Sinister type didn't eat filling in pies (6)
I believe the answer is:
leftie
'sinister type didn't' is the definition.
I know nothing about this answer so I can't tell whether this works.
'eat filling in pies' is the wordplay.
'eat' becomes 'left' (I can't justify this - if you can you should give a lot more credence to this answer).
'filling in' indicates the central letters (the content or filling of the word).
The centre of 'pies' is 'ie'.
'left'+'ie'='LEFTIE'
Can you help me to learn more?
(Other definitions for leftie that I've seen before include "socialist" , "Person with radical tendencies (informal)" , "supporter of "gauche"?" , "Red" , "A radical (colloq.)" .)