Stocky bumpkins in first part of trashy film (8)
I believe the answer is:
thickset
'stocky' is the definition.
(I've seen this before)
'bumpkins in first part of trashy film' is the wordplay.
'bumpkins' becomes 'hicks' ('hick' can be a synonym of 'bumpkin').
'in' means one lot of letters goes inside another.
'first part of' suggests taking the first letters.
'film' becomes 'et'.
The first letter of 'trashy' is 't'.
't'+'et'='tet'
'hicks' put into 'tet' is 'THICKSET'.
(Other definitions for thickset that I've seen before include "Strapping" , "Brawny" , "Heavily built" , "Solidly built; stocky" , "sturdy" .)