This setter is breaking unsuitable lifting instrument (7)
I believe the answer is:
timpani
'instrument' is the definition.
(timpani is a kind of instrument)
'this setter is breaking unsuitable lifting' is the wordplay.
'this setter is' becomes 'Im' (the setter is the person who set the crossword).
'breaking' is an insertion indicator.
'unsuitable' becomes 'inapt' (I've seen this in another clue).
'lifting' is a reversal indicator.
'inapt' written backwards gives 'tpani'.
'im' going within 'tpani' is 'TIMPANI'.
(Other definitions for timpani that I've seen before include "Set of kettledrums" , "set of instruments" , "Percussion instrument" , "Tina Pim has a set of kettle drums" , "orchestra members" .)