Penalties are expected in response to a brawl between crew members of Andretti Green Racing and Team Penske following a post-race confrontation between Sam Hornish Jr and Tony Kanaan at Watkins Glen International on Sunday.
IRL officials reported no injuries or arrests, but indicated sanctions would be handed down later this week.
The incident began when Kanaan, angered by an on-track run-in with Hornish Jr, swerved his No. 11 AGR Honda/Dallara in the direction of Hornish's No. 6 Penske Honda/Dallara as the two cars entered the pits side by side following the end of the race.
"For whatever reason, he decided to be a poor sport about it," Hornish said. "I've been bumped before, too, but I haven't run into people coming into pitlane."
The two cars were then stopped - still side by side - by a race official about halfway down pit road.
Both drivers got out of their cars and began a heated verbal exchange. The incident turned violent when Hornish's father, Sam Hornish Sr, stepped in and pushed Kanaan.
"When you bring your dad to the track to defend yourself, that's what happens," Kanaan said. "He's an old man. I'm not going to beat an old man."
An unidentified man then tackled Hornish Sr, and IRL security director Charles Burns quickly escorted that man, who IndyCar officials declined to identify, over pit wall and out of the area.
At that point, crew members from Team Penske and Andretti Green Racing began punching and shoving each other while Kanaan and Hornish Jr were separated.
"We were not going to fight," Kanaan said. "I was not going to punch him. We were obviously both hot, and we were talking about what happened, and I think they should have let us talk about what happened.
"But then his dad got in the way and bumped me. That's why dads should be in the grandstands and not in the pits."
Kanaan and Hornish collided earlier in the race, and Hornish's car had a large doughnut on the right sidepod from the incident, which cost Kanaan two positions.
Kanaan, angered by the collision, caught up to Hornish as the two cars entered the pits. He swerved right into Hornish's path, and Hornish swerved to avoid a collision.
"You talk about it, you don't just try to run somebody into the wall," Hornish said. "That's idiotic. It was something that happened 30 laps ago. If you're not cooled down by that time, you're never going to be."
If the sanctions involve driver points, they could be costly for both drivers.
Kanaan is third in the IndyCar Series standings, 75 points behind leader Dario Franchitti. Hornish is fifth in the standings, 97 points behind.