About Umpire Signals
When I first started coaching Little League, I was keen on getting the kids well practiced in the basics: hitting, throwing, fielding and so on. As for teaching them the rules of the game, I mostly focused on things that wouldn't get them or the team in trouble, like being careful to tag up on fly balls.
And then I noticed a boy who always seemed confused when at bat. He didn't understand how balls and strikes were called. For him it was nothing but voodoo. I worked with him more and explained the concept of the strike zone, brought in books with diagrams and he figured it out and became a better batter. But I also learned he didn't understand any of the hand signals that an umpire makes and a few of the other kids on the team didn't really know them either. So we formed a circle like we would when we stretched out and we practiced the hand signals. After that review it seemed like the boys were more attuned to the flow of the game.
Hand signals in baseball were introduced to the game during the career of outfielder William "Dummy" Hoy (1888 to 1902). He was the first deaf/mute player to play in the major leagues.