Something packing a punch is in the paper (4)
I believe the answer is:
fist
'something packing a punch' is the definition.
(fists are used to punch people)
'is in the paper' is the wordplay.
'in the' is an insertion indicator.
'paper' becomes 'ft' (Financial Times newspaper).
'is' placed within 'ft' is 'FIST'.
(Other definitions for fist that I've seen before include "One may deck in a ring" , "Bunch of fives" , "handwriting?" , "Hit with a clenched one" , "duke" .)