Based on the Vegas odds (commonly set at +4000 for Rousey), it’s not that far out of order to say Holly Holm defeating Ronda Rousey for the UFC women’s championship was the upset of the century so far. Looking at tape, it becomes obvious how this happened.
Holly Holm was not only a skilled boxer, but she dominated the punching as a lefty. In addition to having to adapt to a Southpaw style, Holm was calm. She would deliver a few good punches at a distance and pull back, staying back from Rousey’s counterattacks and even using Rousey’s aggressiveness to draw her right into the next combination.
By dominating the ring early, forcing patience, and waiting for a frustrated Rousey to make a mistake, Holm established control early and kept it all the way to victory.