Stuart, you asked a serious and subtle question which deserves a thoughtful response.
You implied very honestly that, apart from being shocked and distressed as anyone would be, you felt out of your cultural depth. I wish that more expats would have that sensitivity to cultural differences which sometimes amount to a gulf.
A Greek’s response? I think that would vary depending on age, gender, whether they were local and knew any of the participants I may be wrong but I think it unlikely that a Greek would head off to the police station in those circumstances.
You’re not Greek, and you can’t and perhaps shouldn’t respond as a Greek would. But as to what a decent foreign citizen should do? Probably err on the conservative side. Respond to the human impulse to take care of the victim, ask if he wants a lift to health centre, home or police station – where it’s down to him to report the incident if he wishes, not you – and leave it at that. If the assailant were still on the scene and there was a stand-off, I think I’d probably put out a restraining hand, and say quietly: ok lad, that’s enough. You’ve made your point.
But then I’ve lived here a long time,I speak the language, I’m female (non-threatening) and ancient (accorded some respect). I also know quite a lot about macho Greek concepts like φιλότιμο, εγωισμός, ντροπί, …enough anyway to realize how little I know, and how probably, ultimately unknowable is the Cretan male psyche to those of us raised in a different culture. So I would stand well clear of any further involvement.
It sounds as if you did everything you could in difficult circumstances, and μπράβο σου for trying to learn from the experience.