Regardless of the arena I think most sports fighters would beat most self defense fighters. Because they train for harder contact, have a generally higher level of overall fitness, and regularly use their techniques against fully resisting opponents. In the street or the ring, I think as a whole, sport fighters are better prepared for combat.
That being said, a self defense fighter can train with hard contact, improve their fitness, and spar against fully resisting opponents. If they do, they will have the edge because they have a wider variety of more devastating techniques. Yes, a sports fighter can strike to vulnerable targets, practice impact grappling, and use weapons. But if they don't train to, regularly, they won't have the same level of technical proficiency as someone who does.
One isn't better than the other. They are different methodologies. And there are MMA fighters and Boxers and Olympic style TKD fighters that can definitely kick my tail. But their training doesn't generally take into account many of the things that we regularly discuss or practice, including the legal ramifications of self defense and using weapons, training against multiple opponents, irregular combat environments based on lighting, terrain, and obstructions, and the incorporation of environmental weapons into your techniques. I don't know what considerations sports fighters train for that I don't, because I don't train for sports competition.
This argument is so tired. Somebody posted a video of an eight year old girl doing an XMA style sword dance at a karate tournament. That isn't the kind of karate I do either, but it doesn't make it invalid. There are a lot of different ways to train, and they are specifically meant for different environments.
The sports fighter may be effective in the street, but he doesn't train for it.
The street fighter may be effective in the ring, but he doesn't train for it.
Why is that so offensive to people on both sides of that coin? It doesn't make any of us, in either camp, more or less capable with what we do. It means we do it for different reasons, with different methods, and different desired goals.
Can an MMA fighter win a street fight? Sure. Can a street fighter win an MMA competition? Sure. Because in the end it has a lot more to do with the individual fighter and the competition he's facing then the style he practices. How you train matters. Why you train matters. Maybe some grapplers don't strike. Maybe some strikers don't grapple. But that doesn't make one better than the other. Go tell Iron Mike that his techniques are crap because he doesn't train for self defense. Personally, even today, I'm not interested in making that mistake. By the same token, there are plenty of killers working for governments all over the world who are plenty dangerous without ever having stepped into the square circle.
If you like what you do, keep doing it. But you're never going to get very far telling other people that what they do is garbage. You're just wasting valuable training time.
-Rob
