Being highly-strung, hit out when crowd at court made hullaballoo (6,6)
I believe the answer is:
tennis racket
'out when crowd at court made hullaballoo' is the definition.
I can't tell whether this defines the answer.
'being highly-strung hit' is the wordplay.
'being highly strung' becomes 'tennis' (I can't justify this - if you can you should give a lot more credence to this answer).
'hit' becomes 'racket' (racketing is a kind of hitting).
'tennis'+'racket'='TENNIS-RACKET'
Can you help me to learn more?
(Other definitions for tennis racket that I've seen before include "bat" , "Service deliverer" , "Sports item" , "Scam at Wimbledon" , "This could help one make a good return" .)