Panathinaikos defeated Olympiakos in the opening game of the Greek League finals on Thursday, and riot police where called to control fans.
Panathinaikos won 69-67, at the home arena of Olympiakos.
Josh Childress, formerly of the NBA's Hawks, scored 23 points in a losing effort for Olympiakos.
"The violence we saw today, will make me think real hard over my future in Europe," said Childress.
He signed a three-year, $20 million deal with the club last July.
The game was delayed nearly 20 minutes with Panathinaikos leading 60-58 and a little more than a minute remaining.
Fans threw a flare, plastic bottles and other items at Panathinaikos' bench during a timeout.