Setter throwing up egg and a piece of chicken (7)
I believe the answer is:
gelatin
'setter' is the definition.
(substance which sets or hardens)
'throwing up egg and a piece of chicken' is the wordplay.
'throwing up' says the letters should be written backwards (I've seen 'thrown up' mean this (in a down clue, letters go up)).
'egg' becomes 'nit' (a nit is an insect egg).
'and' means one lot of letters go next to another.
'piece of chicken' becomes 'leg' (chicken legs are eaten).
'nit'+'a'+'leg'='nitaleg'
'nitaleg' backwards is 'GELATIN'.
(Other definitions for gelatin that I've seen before include "Tag line (anag.); glue" , "Setter" , "Jelling agent" , "Colourless protein extracted from animal bones" , "something gluey" .)