Stop briefly, by the sound of it, turn back and exchange it (4)
I believe the answer is:
swap
'back and exchange it' is the definition.
I can't tell whether this definition defines the answer.
'stop briefly by the sound of it turn' is the wordplay.
'stop briefly' becomes 'pause' (I've seen this in another clue).
'by the sound of it' shows a homophone (sound like).
'turn' says the letters should be written in reverse.
'pause' sounds like 'paws'.
'paws' in reverse letter order is 'SWAP'.
Can you help me to learn more?
(Other definitions for swap that I've seen before include "Exchange, substitute" , "Fifty-fifty odds" , "Exchange; hands back" , "Exchange for paws" , "Exchange, barter" .)