Extra purchase, by the sound of it (3)
I believe the answer is:
bye
'extra' is the definition.
(cricket term)
'purchase by the sound of it' is the wordplay.
'purchase' becomes 'buy' (buy is a kind of purchase).
'by the sound of it' shows a homophone (sound like).
'buy' sounds like 'BYE'.
(Other definitions for bye that I've seen before include "Cricketing extra" , "Reason not to play" , "Get one to advance to the next round without playing an opponent" , "Run scored in cricket from unhit ball" , "Law of the local authority" .)