We already know that Maniac has a good background in baseball and the skill to stun both teammates and observers (See Chapter 7 and his bout with McNab).   When Maniac meets Grayson, the retired minor league player, he wants to hear more about his friends experiences playing the game.

In Chapter 26, Grayson tells Maniac that he has

 only one (pitch) left in his repertoire from the old days.  He called it the "stopball" and it drove Maniac crazy.'

      The old man claimed he discovered the stopball one day down in the Texas League and that he was long gone from baseball when he perfected it.  Unlike most pitches, the stopball involved no element of surprise.  On the contrary, the old man would always announce it.

     "Okay... here she comes.  Now keep your eye on her, 'cause she's gonna float on up here, and just about the time she's over the plate, she's gonna stop.  No, nobody else ever hit is so don't you go gettin' upset if you don't neither."

The "stopball" is a device that helps bind the friends to each other.  It is a metaphor for the deliberate approach both take to life, and how each can surprise people and make them see with new eyes. 

The most important thing, however, is about the stopball is that when Maniac finally manages to hit it, Grayson gives in and allows the boy to teach him to read.