Fifty in the main uprising - they are drunk (4)
I believe the answer is:
ales
'they are drunk' is the definition.
The definition suggests an adverb but the answer is not.
'fifty in the main uprising' is the wordplay.
'fifty' becomes 'l' (Roman numeral).
'in the' means one lot of letters goes inside another.
'main' becomes 'sea' (the main is an old name for the sea).
'uprising' says the letters should be written backwards.
'l' placed into 'sea' is 'sela'.
'sela' in reverse letter order is 'ALES'.
Can you help me to learn more?
(Other definitions for ales that I've seen before include "Types of beer" , "What might be delivered by pumps" , "Alcoholic drinks" , "A sale of beers" .)