Unruly geezer once sober causes misery (8,7)
I believe the answer is:
ebenezer scrooge
'misery' is the definition.
(miserable character in Dickens' A Christmas Carol)
'unruly geezer once sober' is the wordplay.
'unruly' is an anagram indicator.
'geezer'+'once'+'sober'='geezeroncesober'
'geezeroncesober' with letters rearranged gives 'EBENEZER SCROOGE'.
'causes' acts as a link.
(Other definitions for ebenezer scrooge that I've seen before include "protagonist in 1a [A CHRISTMAS CAROL]" , "mean-spirited miser" .)