Every sport the ones who are considered the best are in my opinion just tougher then those who might barely get any playing time. Besides the pain tolerance to be on the field / rink / ring etc more, they also have the ability to adjust to the higher pressured games. Like Lebron James is more like Magic Johnson the comparison was with his pass first tendency but critics compare him to Michael Jordan because of the athleticism.
& Allen Iverson had a press conference where the media asked him about not practicing & he was like why bother pretty much his sentiment. Plus he grew up most likely watching teams and players like the Detroit Pistons who would throw Jordan to the floor and what not; And when he played there where the centers like; Shaq, Tim Duncan & David Robinson, ****mbe Mutombo etc etc. Plus I never really payed to much attention to the rules that allowed for hand checking.. But I'd imagine they could practice but between the centers that would try to prevent every lay-up and dunk, no amount of practicing jump shots would be worth it for a majority of the older generation.
The most skilled professional athlete is Muhammad Ali to me though. From that phantom knockout with Sonny Liston, I doubt a old school boxer like that would just throw a fight. And then you take into account that the people in the actual arena couldn't really tell with everyone in agreement what really happened. Plus that fight with George Foreman that Ali used the Rope A Dope" to win. The clip I saw Ali let Foreman back him in the corner & pretty much was smiling and laughing at him. You would think George Foreman known for his punching power would worry Ali enough but; Muhammad Ali didn't even bother to clench his jaw shut. Overall though the toughest & skilled, person ever known for anything associated with a sport is - Bruce Lee.
Like the movie - Enter The Dragon based on his life. There is that scene where the opponent Bruce Lee just beats him & the he gets cheap shotted in the spine. But it was supposed to cripple him to a point that the scenes portrayed he would never able to push himself in a wheelchair. Plus those written accounts of him kicking another adult, ten to fifteen meters in the air to a point that they end up that distance away from Bruce Lee; I doubt his family would lie about what is portrayed just to make him appear cooler. How they were so quick to denounce Tarantino and his mockery of a hollywood movie about him.
To me there's a real definitive reason that all time legends loved and respected him enough to want to train / associate with the man.. Whether it be men like Kareem Abdul-Jabbar to Muhammad Ali stating on the record he utilized what he learned from Lee to [Intercepting Punch]. The documentary video I watched, Ali said after he used the fighting concept to win a boxing match. Ali said he never lost another match for the rest of his career in the heavy weight division. And all the others involved in the sport of anything boxing / combat sports; Myself [You] can see they way the person talking about Bruce Lee knows to that person themselves with one hundred percent confidence - Bruce Lee is a person that transcends every so called greatest.