Stewart's fine falls under Section 12 of the rule book, specifically member conduct guidelines.
According to Section 12.8.1, actions that could result in a $10,000-$50,000 fine include disparaging the sport and/or NASCAR's leadership, or verbal abuse of a NASCAR Official, media members, fans, etc.
Stewart announced earlier Thursday that he would return to the No. 14 Chevrolet this weekend at Richmond after missing the first eight races due to injury.
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