Look up engaging American metal performances (8)
I believe the answer is:
Here is my best explanation:
'performances' is the definition.
(matinee is a kind of performance)
'look up engaging american metal' is the wordplay.
'look' becomes 'seem' (synonyms).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'engaging' means one lot of letters goes inside another.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'metal' becomes 'tin' (tin is a kind of metal).
'seem' backwards is 'mees'.
'mees' placed around 'atin' is 'MATINEES'.