Two cups overturned following half Arabic source of fizz (6)
I believe the answer is:
bicarb
'source of fizz' is the definition.
The definition suggests a singular noun which matches the answer.
'two cups overturned following half arabic' is the wordplay.
'two cups' becomes 'bra' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'overturned' is a reversal indicator.
'following' is a charade indicator (letters next to each other).
'half' indicates taking half.
'bra' back-to-front is 'arb'.
'arabic' with half the letters taken is 'bic'.
'arb' after 'bic' is 'BICARB'.
Can you help me to learn more?
(Other definitions for bicarb that I've seen before include "Digestive remedy (abbr)" , "Antacid" , "Salt" , "Baking soda (abbr)" , "Raising agent in baking (colloq.)" .)