In the end, Mr. Heraskevych would not be dissuaded, so his accreditation to compete in the 2026 Milan Cortina Olympics was withdrawn on Thursday morning shortly before his first run. The IOC says the helmet violates its rules, which prohibit athletes from engaging in messaging on the field of play, in the Olympic village, or during medal ceremonies. Mr. Heraskevych said he is considering appealing the decision to the Court of Arbitration for Sport.