Eat away, having some ketchup (4)
I believe the answer is:
etch
'eat away' is the definition.
(I've seen this before)
'some ketchup' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'ETCH' can be found hidden inside 'ketchup'.
'having' is the link.
(Other definitions for etch that I've seen before include "Carve into surface, impress deeply" , "Prepare artwork" , "Cut design onto metal using acid" , "Design by eating out" , "Engrave deeply" .)