Glowering milk producer's cast out (8)
I believe the answer is:
scowling
'glowering' is the definition.
(I've seen this before)
'milk producer's cast out' is the wordplay.
'milk producer' becomes 'cow' (I've seen this before).
'cast' becomes 'sling' (slinging is a kind of casting**).
'out' means one lot of letters goes inside another.
'cow' inserted within 'sling' is 'SCOWLING'.
(Other definitions for scowling that I've seen before include "Frowning with displeasure" , "glowering" , "looking displeased" , "Lowering" , "looking unhappy?" .)