Intelligence Quotient. IQ. By definition, it is a measeure of intelligence, not necessarily instinct. (Granted, it is now felt to be not very accurate or perhaps fair). If a someone is 23,24 years old, and has been playing baseball since a child..... and they still are making bad decisions as to the rules of the game and what to do from any base in any situation on the basepaths or in the field, then they just haven't been paying attention. They are not inexperienced just because they are now playing against the best players instead of not as good players at others levels. The rules and moves haven't changed. If they haven't learned the game by that age, they must have a low baseball IQ. They are doing the best they can, they just don't have the brain power to do what is needed in the split second without even more repetition. Some learn with one or two repetions. High IQ. Some it takes a lot more. Lower IQ. Some make the same mistake over and over, Low IQ. Same with learning music and the difference between a great "player" and a mediocre player. Some can learn the piece a lot quicker than others, and memorize it quicker and get it from the left side of the brain to the right side of the brain and free themselves to really play the music instead of read the music and have to think about it. High IQ. Some always just read instead of play. That works fine in an orchestra, where your always have sheet music in front of you. All can perhaps get there, but some get there with less repetition. Great jazz guitarist, John Abercrombie, said that the more he played, the quicker it was to learn a new piece and get it from the left to the right side of the brain, where he no longer needed to think and it was just there to add all the emotion and nuance to, or "play". The more he did it, the faster the process got for the next piece he learned - the faster he was able to get it to the right side where he didn't have to think. Doctors, especially surgeons, pilots, we hope they all have high IQ, and can make decisions innately in high stress situations that may require creative action (right brain) and summon the vast accumulated knowledge (left brain) to be, literally, at ones fingertips. You can get by without being the smartest on the baseball field, but you may have to have more repetitions. It might not make you smarter, but it will make you able to not think and still know what to do fast enough to excel.