In California, athletic and amusement event entry fees are
explicitly "excluded by definition" from the sales tax (p. 19: "no exchange of tangible [...] property"), as is merch that comes bundled with the entry fee, such as T shirts ("transfer of property is incidental", ibid.).
Glad to hear Cascade OC, Sammamish OC, EWOC, MerGeo, Evergreen/4DRacing, and the rest of our friends in Washington are apparently safe from back collections!