Get depressed over cereal (4)
I believe the answer is:
sago
'cereal' is the definition.
(I've seen this before)
'get depressed over' is the wordplay.
'get depressed' becomes 'sag'.
'over' becomes 'o' (cricket abbreviation).
'sag'+'o'='SAGO'
(Other definitions for sago that I've seen before include "Starchy food as white pudding" , "Powdery starch used in cooking" , "Type of milk pudding" , "Edible palm starch" , "Cereal, used in pudding" .)