Hailie Deegan was puzzled. She had come to stock-car racing from the rough-and-tumble world of off-road racing, where she considered herself to be just one of the guys. Off-road racers slammed into one another and knocked each other over, then left the track and laughed about it.

She found stock-car competitors, also mostly men, to be different. She would drive in a straight line down the middle of the track and be put into the wall for no apparent reason, and no one hung around after the race to laugh about it. Or even discuss it.

“I was trying to control it, but I just went from being swung at, to swinging,” Deegan said. “That’s what stock-car racing is. You hit someone, or you get hit. That’s something I had to learn. It’s a key factor in why I’m so aggressive. I don’t want to have to hit you. But if you’re going to hit me, I’m going to hit you.”

Deegan, who turned 18 in July, is the highest-profile woman driving in NASCAR since Danica Patrick. A regular in the K&N Pro Series, which is essentially the rookie league of stock-car racing, Deegan has won three of her 35 races. She also has driven in four races in the ARCA Menards Series, one step up, with two top-10 finishes.