Nike did not say why the contract offer was rescinded, only that Walker “did not take up this option in a timely manner.” Walker put his gear up for sale on eBay.

Mike Hazle, the 2011 American champion in the javelin, said his Nike-made shoes were too narrow, causing his toenails to fall off and his feet to become numb. So for years, he said, he borrowed gear made by Asics and Li-Ning, a Chinese company, from a fellow javelin thrower. He covered those logos with tape or with slices from wristbands that bore the Nike swoosh.

It was never a problem in the little-noticed event, Hazle said, until he won the United States title and a photograph of him appeared in Track & Field News. His left foot was raised after a throw, revealing the check-mark logo of Li-Ning on the bottom of his shoe.

Nike was not pleased and exercised an option on his contract in 2012 to keep him from signing with another company, Hazle said, but offered only $10,000 with no chance of bonuses.

It is unfortunate “if someone is paying your bills and you’re supposed to wear what they give you and it doesn’t work,” Hazle said from Afghanistan, where he is serving in the Air National Guard. “But at the end of the day, it’s going to compromise your performance, so you’ve got to take care of yourself.”

Nike said it did not comment on contracts but expected that its sponsored athletes “will always wear Nike products unless there is some specific, mutually agreed exception.”