Tricky grasping instrument suddenly (7)
I believe the answer is:
sharply
'suddenly' is the definition.
(thesaurus)
'tricky grasping instrument' is the wordplay.
'tricky' becomes 'sly' ('sly' can be a synonym of 'tricky').
'grasping' is an insertion indicator.
'instrument' becomes 'harp' (harp is a kind of instrument**).
'sly' going around 'harp' is 'SHARPLY'.
(Other definitions for sharply that I've seen before include "In an aggressive manner" , "Crisply" , "Very suddenly and to a great degree" , "Punctually" , "Critically" .)