It started with a drawing that didn't work.
One night after a game, a dad sat at the kitchen table with his boys, trying to explain the play that beat them. Runners on first and third. Ball hit to short. What you do depends on the situation: whether it is on the ground or in the air, and whether third is breaking for home. Everything after that changes with it. Paper. A hand-drawn diamond. Arrows, then more arrows, then arrows crossed out. The boys wanted to learn, and they were completely lost. The explanation was making it worse.
Ball 101 is that drawing. Animated, interactive, and finally understandable.