Eat some ketchup (4)
I believe the answer is:
etch
'eat' is the definition.
(I've seen this before)
'some ketchup' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ETCH' is hidden within 'ketchup'.
(Other definitions for etch that I've seen before include "Use acid to cut design" , "Make incisions" , "Engrave deeply" , "Score deeply" , "Cut; engrave" .)