Baseball is an integral part of Wilson's drama.  On one hand, the structure of the play is relevant to baseball.  Troy's life is depicted in nine scenes.  To an extent, this corresponds to how Troy's life unfolds with a beginning, middle, and end similar to baseball games.  I think that the full extent of baseball on Troy's life comes out of Scene Three.  It is at this moment that we see Troy attempt to shut down Cory's hopes of playing football.  Rose brings out that the child's pursuit of his dreams is similar to the father's previous dream of playing baseball.  The recognition gained from this moment is that baseball was something pure in a world of impurity for Troy.  Whereas his relationship with his father was filled with abuse and neglect, at best, and Troy's world was replete with individuals who used him as a means to an ends and not an end in his own right, baseball was pure.  Troy saw baseball as something that could rectify the wrongs of the universe and when it turned on him, in terms of rejecting him because of his age in the newly integrated leagues, a bitterness settled into his own psyche that made it impossible to overcome.  In some respects, baseball might have been the last thing that Troy really loved.  Its departure helped him to construct "fences" between he and the world that causes him so much in pain and between people with whom he cannot help but cause pain.