Kathrine Switzer was attacked 50 years ago as she ran the Boston Marathon. The reason? She was a woman.

Kathrine Switzer was a few miles into her history-making run at the Boston Marathon on April 19, 1967, when Jock Semple, the co-director of the famous 26-mile race, suddenly appeared behind her and tried to shove her out of the competition.

Semple’s lunge at Switzer was captured by national news photographers. What happened next changed running forever.

Switzer’s boyfriend, Thomas Miller, threw a block that knocked Semple out of her way, allowing the 20-year-old runner from Syracuse University to finish the race in 4:20:02 at a time when women were thought to be too fragile for long-distance running.

Semple later disqualified Switzer for, among other things, running with the men. She’d registered under the name “K.V. Switzer” not with the intention of becoming a women’s pioneer in the sport but to prove to her coach, Syracuse’s Arnie Briggs, that women could run 26.2 miles.

“What happened to me was a radicalizing experience. And it was one that made me bound and determined to change things for women,” she told the Boston Globe. “Running had given me everything, and I wanted other women to feel that as well.

On Monday, Switzer, now 70, ran the Boston Marathon again. And this time, she was greeted with acclaim instead of consternation.

Switzer, who won the 1974 New York City Marathon, successfully campaigned for the women’s marathon to become an Olympic sport in 1984. In 2015, she started a nonprofit, 261 Fearless, that uses running to empower women around the world.

And her story continues to inspire women 50 years later. Her bib number from the 1967 Boston Marathon – 261 – is sometimes worn by women on their arms when they race. Others have had it tattooed on them.

”It obviously meant so much to them to have this sense of fearlessness,“ Switzer said of what her bib number represents. ”They’ve really inspired me that way.”