USA Today

Excellence. Fundamentally, it's why we watch sports, to see human beings reach their ultimate potential, to see the body and mind pushed to their absolute limits.

Everyone in athletics searches for it, for those few moments that remind us of everything we can be. Finding it, sometimes in unexpected places, justifies the endless hours we spend watching other people engage in mostly meaningless competitions and pursuits.

In the UFC, true excellence emerges only rarely—that intersection of heart, spirit and athletic ability. It's the flick of an Anderson Silva front kick. It's the economy of motion in Georges St-Pierre's Superman punch. It's Matt Hughes running across the Octagon, Frank Trigg on his shoulder like a sack of oats, looking for the hardest spot he can find to drop him.

It's Ronda Rousey.

In some ways, the UFC couldn't have asked for a better ambassador to launch its bold foray into women's fighting. Famously described by Dana White as a "dude trapped in this beautiful body," Rousey is the perfect bridge to integrate women into the UFC. She's undeniably a woman, beautiful and sporty, but not in a way that's distractingly feminine to some less enlightened minds.

Rousey is easy to understand, her motivations as simple and myopic as any male fighter. Seek and destroy is her motto, and her success in that endeavor is inarguable. An incredible athlete, Rousey is strong, fast, teachable and adaptable.

She's a born fighter, trained from an early age by a mother who would wake her from slumber in a sneaky armbar attempt. She's won every fight she's ever had, all but one in the very first round. Sara McMann, supposedly her physical equal, an Olympian with a resume just as long as Ronda's, was dispatched almost as an afterthought, a training dummy to try out new techniques on, a punching bag with an Olympic medal dangling.

When it comes to demonstrating women's capability for combat, Rousey stands on a pedestal with a handful of Marines, some helicopter pilots and Joan of Arc. She's earned her respect, forcefully establishing women as equal partners in the UFC hierarchy.

Her status, despite some claims to the contrary, was no gift. She earned it in the cage, her athletic prowess undeniable to all but the most staunch misogynists. She's brought the entirety of the women's sport with her, easing what might have otherwise been a difficult transition.

But with that excellence comes no small amount of difficulty, especially for UFC matchmakers. Rousey is so amazing, on every level, that it's hard to imagine anyone else as her equal. She outgunned McMann. She dispatched Miesha Tate with ease. These fights weren't just one-sided—they barely even seemed fair.

Worse, it's hard to picture future title challengers doing any better against Hurricane Ronda. Rousey is a queen with no court. There is no looming challenger—at least none in the UFC, where Alexis Davis and Cat Zingano do little to get anyone's blood racing.

There is, however, another.

Before Rousey, there was an earlier snarly, muscle-bound champion, a force unlike anything women's MMA has seen before or since. While Rousey has concentrated her brilliance on the ground, Cris "Cyborg" Justino made her bones on her feet, battering opponents with a stand-up attack at times technical, at times little more than barely contained rage.

She's the truly fearsome opponent Rousey needs, that fans need, to continue building interest in women's MMA. It's the classic battle that has defined the sport from its inception—the striker versus the grappler. It's size and strength against technique and cunning. It's the kind of fight that makes stars into legends.

And it's a battle we may never see.

UFC promoter Dana White sits on very dangerous ground. Rousey is, by his own admission, the whole reason he's in the women's MMA game in the first place. She has the potential for greatness, in the cage and at the box office, and he's undoubtedly terrified at the very thought of her losing a fight at this stage in the building process.

But there's also danger in babying a fighter too much. Fans can sense when a fighter is being protected, and they don't respond kindly. Rousey's potential, in fact, may be squandered without a true foil to test her. It's only fire that produces a fighter worth embracing, the flames of competition hardening steel and forging champions.

Without Cyborg or another great challenger, Rousey only has the potential for greatness. With Cyborg across the cage, she can actualize it, reaching her true potential as an athlete and a drawing card.

Women's MMA needs Rousey. And Rousey needs a challenge. She needs Cyborg. We all do.