I can remember a few knuckleball pitchers that were really effective. One for the Rangers. If I remember correctly, some of the pitchers extended their careers by learning to throw it. I also remember the Rangers would not allow the knuckleballer to throw in practice because it tended to miss up the batter's swing. Catchers usually used an oversized mitt to try to catch it. I had one thrown at me one time when I was not expecting it as a joke and I was lucky to catch it.