Complain about the meat (4)
I believe the answer is:
beef
This clue is a double definition.
'complain' is the first definition.
(beefing is a kind of complaining)
'the meat' is the second definition.
(beef is a kind of meat)
'about' is the link.
(Other definitions for beef that I've seen before include "Grumble - muscle" , "Brawn; complaint" , "joint, perhaps" , "Grumble over cattle meat?" , "it's unacceptable for vegetarian" .)