At the trial, Dietrich’s victim said he was dancing with his girlfriend at Bungalow bar about 2.30am when an unidentified older man grabbed her bottom.
After she complained to security staff, the victim approached the bouncers as they were talking to the man and his two companions, one of whom was the defendant.
His intention had been to check if they knew which of the men had grabbed his girlfriend, but he lost his temper and pushed the older man in the chest.
The defendant then headbutted him, sparking a brief flurry of punches between the pair.
Giving evidence at the trial, Dietrich said the victim had been "super-aggressive" when he came over and pushed the older man, whom he had only met that night.
He had exchanged words with the victim, who asked him "do you want a go then?".
Although he accepted he "overreacted", the headbutt was a reflex action when he thought he was about to be attacked.
"It was a split-second.
"He was walking towards me, balling his fists."
At yesterday’s sentencing, counsel Tanya Surrey told Judge Brian Callaghan the defendant was on an interim work visa, but intended to apply for residency once the charge was dealt with.
A conviction would reduce the likelihood of that application being successful.
She asked Judge Callaghan to consider the defendant’s relative youth, clean criminal record in New Zealand and his home country, and the lack of premeditation behind the assault.
Having to leave New Zealand was a "potentially devastating" consequence of a conviction, Ms Surrey said.
"He accepts this was a foolish mistake, but hopes it doesn’t define his future."
Judge Callaghan said the headbutt was a "reactionary, spontaneous assault that arose in very unusual circumstances".
The defendant had "completely overreacted", and any attack to the head was serious.
The central issue was the impact of a conviction on the defendant’s immigration status.
Even if he granted a discharge, Dietrich would face difficulty gaining residency or further visas.
A conviction would also have consequences for his future employment prospects.
He granted the discharge, ordering the defendant to perform 150 hours’ community work and pay the victim reparation $1500 for emotional harm.
