Jock Semple

John Duncan Semple (October 26, 1903 – March 10, 1988) was a Scottish-American runner, physical therapist, trainer, and sports official. In 1967, as a race official for the Boston Marathon, he attempted to stop the 20-year-old marathon runner Kathrine Switzer from continuing to run and knocked down her coach when he tried to protect her. Switzer was officially entered in the race in accordance with the Boston Marathon's rule book, which at that time made no mention of sex. Semple subsequently claimed that amateur rules banned women racing for more than . He subsequently oversaw implementation of qualifying times in 1970 and, in response to lobbying and rule changes by the Amateur Athletic Union (AAU), the implementation of a separate women's race in 1972. ahead of two-thirds of the runners. Another woman, Kathrine Switzer, completed the 1967 race having registered officially. Although the Boston Marathon rule book made no mention of sex, Switzer's boyfriend Tom Miller managed to shove Semple aside after Semple had knocked Switzer's slightly-built 51-year-old coach to the ground when he attempted to protect Switzer; both Miller and Switzer's coach were competing in the race alongside Switzer.

Later in life, Semple reversed his position on women competing in the marathon. According to Marja Bakker (a later organizer of the race), "Once the rule was adjusted and women were allowed in the race, Jock was one of their staunchest supporters. He was very progressive." Semple later publicly reconciled with Switzer. "Old Jock Semple and I became the best of friends," she told a reporter in 2015. "It took a long time: six years. But we became best of friends."

In 1981, he published an autobiography, Just Call Me Jock. He was inducted into the RRCA American Long Distance Running Hall of Fame in 1985.

Semple died of cancer of the liver and pancreas in March 1988 in Peabody, Massachusetts. He and Kathrine Switzer had become friends and she would visit him at the hospital where he was being treated for his cancer. The Jock Semple Award given by the Boston Athletic Association is named in his honor.