Both drivers also were placed on probation, with NASCAR saying the penalties "are about maintaining a safe environment following the race." Matt Kenseth and Denny Hamlin were not penalized for their roles in the skirmishes after Saturday night's race.
"We knew that the new Chase format was likely going to raise the intensity level, and we want our drivers to continue to be themselves," said Robin Pemberton, NASCAR senior vice president of competition and racing development. "However, the safety of our drivers, crew members, officials, and workers is paramount and we will react when that safety could be compromised."
The sequence of events began on the cool-down lap when Hamlin admittedly brake-checked Keselowski to show his displeasure with how Keselowski raced him over the final two laps. Keselowski then tried, but failed, to spin Hamlin.
He then hit Kenseth's car as they traveled toward pit road in an act of retaliation, Keselowski said, for Kenseth driving across the front of his car under caution with six laps remaining in the race. Keselowski inadvertently ran into the back of Stewart's car as the entire field headed toward pit road. Stewart responded by backing his car up into Keselowski's car.
Keselowski then drove around several stopped cars and into the garage, with Hamlin following in his car. The two drivers cut through an empty garage stall before coming to a stop, and Hamlin had to be restrained from confronting Keselowski.
As Keselowski walked between two team haulers, Kenseth rushed in from behind and jumped him. Crew members quickly peeled Kenseth away, and he made it clear he was upset Keselowski hit him while his seatbelts were off and his window net down. Keselowski could be heard on video yelling: "You hit me under yellow!"
Hamlin, Kenseth and Keselowski are competing for the Sprint Cup championship, and poor finishes Saturday night have Kenseth and Keselowski on the brink of elimination. The pressure of the Chase, which this year debuted an elimination format that cuts four drivers after every third race, has been singled out as a contributor to the mayhem at Charlotte.
"There's incredible pressure for everyone involved in that Chase right now," Clint Bowyer said from Tuesday's test at Phoenix. "It's literally a knockout round."
Hendrick Motorsports driver Jeff Gordon praised the show of emotion -- "The fans love it, the media loves it, sometimes our emotions just get away from us," he said -- while teammate Dale Earnhardt Jr. thought Saturday night brought more attention to NASCAR.
"I think that's good for the sport, at least in the short term," Earnhardt said.
Stewart, meanwhile, did not qualify for the Chase for the Sprint Cup championship. His involvement -- however brief -- put the three-time champion back in the spotlight. He sat out three races in August after a sprint car he was driving struck and killed Kevin Ward Jr. at a dirt track in upstate New York; a grand jury decided he would not be charged in Ward's death.
"It's unfortunate Stewart got dragged into this," said Hall of Famer Darrell Waltrip, now a Fox analyst. "Because of the incident in New York, the media know who Stewart is, saw what happened and jumped to their own conclusions and made judgments. That's unfortunate because Stewart had nothing to do with what happened on Saturday night."
The penalties for Keselowski and Stewart are in line with past punishments for drivers who used their cars to retaliate. NASCAR did not find that Hamlin deserved to be punished for following Keselowski through the garage in his car, an act many onlookers deemed dangerous in a crowded and dark work space.
NASCAR also didn't follow precedent in not fining Kenseth. Both Marcos Ambrose and Casey Mears were fined in May for fighting in the garage, but Ambrose threw a punch in that situation. There was no evidence Kenseth threw a punch on Saturday night.