Wood being crushed by stone instrument (6)
I believe the answer is:
spinet
'instrument' is the definition.
(spinet is a historical type of musical instrument)
'wood being crushed by stone' is the wordplay.
'wood' becomes 'pine' (pine is a type of wood).
'being crushed by' is an insertion indicator.
'stone' becomes 'st' (abbreviation).
'pine' going inside 'st' is 'SPINET'.
(Other definitions for spinet that I've seen before include "Instep (anag)" , "Step in with old musical instrument" , "Small 12" , "Type of early harpsichord" , "organ" .)