Cry, being fat (7)
I believe the answer is:
blubber
I believe this clue is a double definition.
'cry' is the first definition.
(blubbering is a kind of crying)
'being fat' is the second definition.
('blubber' can be similar in meaning to 'fat')
(Other definitions for blubber that I've seen before include "Cry uncontrollably" , "Cry -- whale fat" , "Your body's fat" , "Break down" , "Fat of sea mammals - cry" .)