From a few eyebrow-raising names and the presence of very obscure "sports" (darts??!?!?), I am going to guess this is a subjective list rather than a quiz based on a more objective list compiled by a sports magazine or media. Makes it very hard to guess. If you want to keep the quiz, I would highly recommend that you make it so it works with only the last names; the vast majority of quizzes on this site and all the featured ones work that way, so nobody ever enters the full name. When Federer, Gretzky, Manning and Jordan didn't work, I thought something had to be very wrong.
Based on statistical records, and darts is one of the most popular and recognised sports, with Taylor the most successful sportsperson of all time based on records, with 16 world titles.