Hooligan left behind London museum (6)
I believe the answer is:
vandal
'hooligan' is the definition.
(I've seen this before)
'left behind london museum' is the wordplay.
'left' becomes 'l' (common abbreviation).
'behind' says to put letters next to each other.
'london museum' becomes 'Vanda' (V and A, Victoria and Albert Museum).
'l' put after 'vanda' is 'VANDAL'.
(Other definitions for vandal that I've seen before include "Someone who destroys or defaces property" , "Hooligan" , "Person who maliciously damages things" , "Hoodlum" , "Ger. tribesman; one who damages property" .)