From what I can find, "track use" isn't in the law, but rather a matter of enforcement discretion.
"The Clean Air Act does not contemplate removing emissions controls from an EPA-certified motor vehicle in order to convert it into a competition vehicle. As a matter of enforcement discretion, the EPA’s longstanding practice has been not to take enforcement action against vehicle owners for removing or defeating the emission controls of their EPA-certified motor vehicles, so long as they can show the vehicles are used solely for competition events and no longer driven on public roads."
"The Clean Air Act does not contemplate removing emissions controls from an EPA-certified motor vehicle in order to convert it into a competition vehicle. As a matter of enforcement discretion, the EPA’s longstanding practice has been not to take enforcement action against vehicle owners for removing or defeating the emission controls of their EPA-certified motor vehicles, so long as they can show the vehicles are used solely for competition events and no longer driven on public roads."
https://www.autoweek.com/news/industry-news/a36482793/sema-e...