In haze, bag up, but put in the wrong hams? (7)
I believe the answer is:
miscast
'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 "having the wrong part" , "Given an inappropriate role" , "Of actor, assigned to unsuitable role" , "in the wrong film?" , "Of actor, unsuited to a role" .)