Immobilise government with sharp, high-pitched sound (4)
I believe the answer is:
ping
'high-pitched sound' is the definition.
(ping can mean a high-pitched noise)
'immobilise government' is the wordplay.
'immobilise' becomes 'pin' (as in to pin someone down).
'government' becomes 'g' (abbreviation for government).
'pin'+'g'='PING'
'with sharp' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for ping that I've seen before include "Abrupt high-pitched ringing sound" , "Short high-pitched sound" , "Sharp ringing sound" .)