how did danny and reuven become friends?

At the beginning of the novel, both are fifteen years old and live near one another, although because they go to separate yeshivas (parochial schools) they have never met. The two meet during a softball game between their two schools, in which Danny confronts Reuven and calls him an apikoros (a Jew who denies the basic tenets of his faith) as Danny is on second base. During the baseball game, Reuven pitches to Danny, who hits the ball back at him, hitting him in the eye and shattering his glasses.