Monkey in a tram going berserk (7)
I believe the answer is:
tamarin
'monkey' is the definition.
(tamarin is a kind of monkey)
'in a tram going berserk' is the wordplay.
'going berserk' indicates an anagram.
'in'+'a'+'tram'='inatram'
'inatram' is an anagram of 'TAMARIN'.
(Other definitions for tamarin that I've seen before include "Main art (anag) - monkey" , "Small monkey of the marmoset family" .)