Everyman's behind essentially nasty fizz (4)
I believe the answer is:
asti
'fizz' is the definition.
'everyman's behind essentially nasty' is the wordplay.
'everyman's' becomes 'sti' (I am not sure about this - if you are sure you should believe this answer much more).
'behind' says to put letters next to each other.
'essentially' says to take the centre.
'nasty' becomes 'bad' (I've seen this in another clue).
The centre of 'bad' is 'a'.
'sti' put after 'a' is 'ASTI'.
Can you help me to learn more?
(Other definitions for asti that I've seen before include "town in Italy" , "Sparkling wine named after an Italian Piedmont town" , "Piedmontese white wine" , "Italian drunk" , "Capital of a north-west Italian province, known for its sparking wine" .)