The game between the long-time rivals started in a tense atmosphere in the Universiada Hall in Sofia with vociferous Levski "ultras", their hardcore fans, standing close behind the visitors' bench, shouting insults at the Balkan staff and throwing plastic bottles.
Tensions increased with three minutes remaining following another confrontation, as the home supporters hurled objects at the Balkan players, including a long stick, and tried to get on court.
Security guards prevented the court invasion and riot police immediately entered the hall while the referee interrupted the match and ordered both teams back to the dressing rooms.
The match officials then said the game could be resumed behind closed doors, but visiting supporters, led by the Botevgrad mayor and ex-Balkan player Ivan Gavalyugov, refused to leave the hall.
Gavalyugov protested against what he called Levski's "irresponsible decision to place their most dangerous fans behind Balkan's bench".
"This is an ugly provocation," Gavalyugov told state broadcaster BNT. "Our opponent deliberately placed the "ultras" behind our bench. Right after the first incidents I told them it would be scary, they have no place there.
"Then I told them at halftime - please, do something... We have come to watch basketball and we believe we have the right to stay up to the end."
Levski, who were leading 66-59 after 37 minutes, also condemned the ugly scenes but refused to accept responsibility for placing their hardcore fans close to the Balkan players.
The domestic league said the remaining three minutes would be played on Thursday behind closed doors.
Levski have a history of fan violence at their football and basketball matches.
In 2014 the Adriatic League match between Levski and Serbia's Partizan Belgrade was interrupted for almost an hour after the end of the first quarter due to fan violence.
Fights broke out in the Universiada Hall’s stands and then more than 100 supporters invaded the court, clashing with security staff and throwing seats, chairs and other objects.
(Reporting by Angel Krasimirov; Editing by Toby Davis)
