Museum initially lambasting hooligan (6)
I believe the answer is:
vandal
'hooligan' is the definition.
(I've seen this before)
'museum initially lambasting' is the wordplay.
'museum' becomes 'V and A' (Victoria and Albert Museum).
'initially' indicates taking the first letters.
The initial letter of 'lambasting' is 'l'.
'vanda'+'l'='VANDAL'
(Other definitions for vandal that I've seen before include "Someone who wilfully damages property" , "Hooligan" , "Person who maliciously damages things" , "One doing deliberate damage" , "Wanton wrecker" .)