Boxer, you heard, punching cook (4)
I believe the answer is:
fury
'boxer' is the definition.
(Tyson Fury is a boxer)
'you heard punching cook' is the wordplay.
'you heard' becomes 'U' (homophone of 'you').
'punching' means one lot of letters goes inside another (inserted letters punch or puncture others).
'cook' becomes 'fry' (frying is a type of cooking).
'u' inserted inside 'fry' is 'FURY'.
(Other definitions for fury that I've seen before include "Hellcat" , "Wild rage" , "Extreme anger" , "Great anger or rage" , "Intense anger" .)