Junkie attacking in Tram in CBD

We were sitting in the tram and suddenly a junkie (around 30 I would guess) came to the young guy sitting next to me and told him he pointed at him (which he obviously didn’t do). Out of nowhere the junkie boxed the young guy in the eye and started shouting, and everyone in the tram ran out except me and another guy who told him to f*ck off. I don’t mind to throw a punch at a junkie but prefer not to. I just moved here so wondering if this is normal occurrence?