Went berserk in rave outside port (3,4)
I believe the answer is:
ran riot
'went berserk' is the definition.
(I've seen this in another clue)
'rave outside port' is the wordplay.
'rave' becomes 'rant' (synonyms).
'outside' is an insertion indicator (some letters go outside others).
'port' becomes 'rio' (Rio de Janeiro is a port).
'rant' enclosing 'rio' is 'RAN RIOT'.
'in' acts as a link.
(Other definitions for ran riot that I've seen before include "Went on rampage" , "Got out of control" .)