The relationship between outcome uncertainty, the superstar effect, talent and live attendance at professional boxing matches is analyzed for forty-three contests. The implied probability the underdog will win (taken from bookmaker odds) is used to model outcome uncertainty, while the time-adjusted average number of Twitter Followers of the combatants in a given boxing match is employed as a proxy for the superstar effect. Utilizing a log-log multivariate regression model (with live attendance as the dependent variable and explanatory variables of outcome uncertainty, the superstar effect, average knockout percentage and a dichotomous variable to capture if one or both combatants is an Olympic Medalist), we find only the superstar effect to have a statistically-significant impact on live attendance for professional boxing matches. These findings support recent evidence from English Premier League Football, the Italian Football League (Serie A and B), U.S. Major League Soccer and the U.S. National Basketball Association that star power is a critical determinant of live attendance and television viewership in professional sports. While owners, managers and marketers go to great lengths to promote competitive balance as a means of generating and maintaining fan interest, the aforementioned findings indicate that greater emphasis should be focused on highlighting the quality of the athletes themselves and, more broadly, their celebrity status.