The spot outside the apartment building in Kallithea where the bloody clash took place at midnight on Wednesday. [Ismini Vlassopoulou/Intime News]

Sport-related hooliganism was behind a fatal stabbing in the Athens suburb of Kallithea, where a young boy was killed after teenagers clashed in a public square shortly after midnight Wednesday, authorities said.

The confrontation erupted in the square of Agia Eleousa, where a group of six to seven teenagers had gathered. The youths did not share a single team allegiance – some supported Olympiakos, others Panathinaikos, and among them was a 16-year-old described as a hardcore AEK fan.

According to police, that 16-year-old had allegedly attacked and wounded an Olympiakos supporter in the leg three to four days earlier – an incident never reported to police. When someone spotted him in the square Wednesday night, a group of five Olympiakos fans drove to Kallithea to retaliate.

A fight broke out between the two groups, during which a 17-year-old suspect fatally stabbed a 15-year-old Olympiakos fan who had come seeking revenge.