In haze, bag up, but put in the wrong hams? (7)
I believe the answer is:
'put in the wrong hams?' is the definition.
(ham can mean an actor)
'in haze bag up' is the wordplay.
'in' is an insertion indicator.
'haze' becomes 'mist' (I've seen this before).
'bag' becomes 'sac' (a small bag).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'sac' in reverse letter order is 'cas'.
'mist' going around 'cas' is 'MISCAST'.
'but' acts as a link.
(Other definitions for miscast that I've seen before include "Of actor, assigned to unsuitable role", "Given an inappropriate role", "part poorly chosen", "Give an unsuitable role", "having the wrong part".)