Honestly after years of contemplating this question I think it’s the geometry. The way that the still scene on the field at any given moment contains a finite but vast number of possibilities. The more into baseball you are, the more of these possibilities you’re able to spot and hold in your mind between pitches. In this way, baseball mirrors literally every waking moment of one’s life, except that in baseball, the compulsion to act is permanent and ongoing, so there’s never a point in any 3-2 count where the whole team just loses sight of its goals and gets a crummy job it hates and ends up wasting a whole year there instead of just the summer. This just doesn’t happen in baseball. There are a number of possibilities, and then one of them is put into play, and then the consequent number of possibilities opened by the play are set in motion, and yet again they are winnowed down to one, and all this is right there, like the energy of the atom, in the configuration of the nine players on the field and the one at the plate. Hence geometry. This is the opposite of boxing, which is not about geometry or physics or calculus or heroic narratives, but which is the sport where you get to hit somebody in the face all night and he doesn’t even take it personally, and then you even hug each other afterwards no matter who won, unless you’re a really bad sport.