The relative standard deviation measure of league parity is persistently higher for the National Basketball Association (NBA) than for the other three major sports leagues in North America. This anomaly spans the last three decades and is not explained by differences in demographic and market characteristics. With a much greater number of scoring attempts in each game, basketball reduces the influence of random outcomes in the number of points scored per game and also season winning percentage. Our simulations demonstrate that lesser parity in the NBA is inherent in the rules of the game so that interleague comparisons must be interpreted carefully.