The baseline is how big and strong you are. Your skill and any experience lets you use that better. I'm not naturally athletic and have almost never actually been in a real fight. But I'm pretty tall and heavy, and do work out at times. I chose 60%, though it should probably be more if you count how much of the population is made up of children and elderly people, and even completely healthy people who are as unathletic as I or are simply smaller or physically weaker, like the majority of women.
The people with the best chance of beating me would be healthy, strong, young people with no physical or mental disabilities. I assume this is a weapons-free fight, so I would say I could beat 85% of the world in a fight.