Tension between basketball fans from Evanston Township High School and New Trier High School escalated to violence outside Welsh-Ryan Arena Friday night after ETHS defeated New Trier 48-44.

The fight comes after years of growing tension between the two schools and parent concern, said Cheerie Hanson, president of the ETHS Parent-Teacher-Student Association.

A group of people wearing ETHS T-shirts assaulted about five New Trier fans Friday night as they were getting into a car parked in front of Mustard’s Last Stand, 1613 Central St.

Between 10 and 15 ETHS fans chased the New Trier fans to the grey sedan and struck them repeatedly with jackets and pompoms. Several people in the crowd of 100 ETHS fans threw snowballs and garbage can lids at the car.

As the crowd of 7,500 spilled out of the arena following the game, supporters of both schools mocked each other in the main parking lot.

Two EPD cars and one University Police car arrived at the scene as the crowd began to disperse, but no police were available for comment.

ETHS Athletic Director John Riehle, said he did not witness the incident and was unaware of similar incidents. But he said increasing civility among the fans is his No. 1 priority.

“We’re very sensitive about students, student athletes and about the image we present,” Riehle said. “I’m very proud of our students.”

Tensions between fans can be attributed to publicity hyping the game as a rematch of rivals, said Keith Woods, a Mustard’s employee who was working Friday night.

The rivalry is dangerous because it perpetuates unnecessary hatred between students, said Eric Weiler, 17, a senior at New Trier.

“If kids are going to get into fights about basketball games, that’s a major problem,” Weiler said.