There seems to be some uncertainty about its origins, with some saying sports, many cite “toeing the plank,” and a few other explanations: https://en.wikipedia

There seems to be some uncertainty about its origins, with some saying sports, many cite “toeing the plank,” and a few other explanations: https://en.wikipedia.org/wiki/Toe_the_line https://en.wikipedia.org/wiki/Toe_the_line