Speak wildly about port, having gone berserk (3,4)
I believe the answer is:
ran riot
'gone berserk' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'speak wildly about port' is the wordplay.
'speak wildly' becomes 'rant' (I've seen this in another clue).
'about' means one lot of letters goes inside another.
'port' becomes 'rio' (Rio de Janeiro is a port).
'rant' placed around 'rio' is 'RAN RIOT'.
'having' is the link.
Can you help me to learn more?
(Other definitions for ran riot that I've seen before include "Went on rampage" , "Got out of control" .)