When there's a panic, Alf turns quiet (4)
I believe the answer is:
flap
'when there's a panic' is the definition.
I can't tell whether this defines the answer.
'alf turns quiet' is the wordplay.
'turns' is a reversal indicator.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'alf' back-to-front is 'fla'.
'fla'+'p'='FLAP'
Can you help me to learn more?
(Other definitions for flap that I've seen before include "Move wings - panic!" , "Minor panic; tab" , "Moving surface on wing" , "Move like a bird or get into a tizzy" , "Adjustable part of wing - panic" .)