Mass decree getting disorderly fellows the booze (5,2,6)
I believe the answer is:
creme de menthe
'booze' is the definition.
(creme de menthe is a kind of booze)
'mass decree getting disorderly fellows the' is the wordplay.
'mass' becomes 'm' (symbol used in Physics e.g. f=ma).
'getting' says to put letters next to each other.
'disorderly' indicates an anagram.
'fellows' becomes 'men' (fellow can mean a man).
'm'+'decree'='mdecree'
'mdecree' anagrammed gives 'cremede'.
'cremede'+'men'+'the'='CREME DE MENTHE'
(Other definitions for creme de menthe that I've seen before include "Green-coloured liqueur" , "Green peppermint-flavoured liqueur" , "Mint flavoured liqueur" , "Sweet green or white liqueur" , "Green liquid" .)