The narrator of The Natural never reveals him- or herself, and s/he takes a hands-off approach to telling the story: no interventions here. Just like the reader, this narrator is on the outside looking in. And much like Lola with her crystal ball, the narrator knows what's going on inside the characters' heads. For example, we get to see what Roy and Sam dream and hallucinate about, and we read a lot about Roy's thoughts and fears.
For example, on the car ride with Memo we find out,
There were times when he thought yes, I am on my way up in her affections, but no sooner did he think that when something she did or said, or didn't do or didn't say, made him think no, I am not. (5.11)
Because this is a baseball novel that's also trying to be Literature with a capital L, the narrator's access into the character's conscious and unconscious minds lets Malamud dig deep into the psychology of Roy et al. This psychic narrator is doing more than giving us a play-by-play of a baseball game; this is a serious, psychological novel that lays bare the motivations of its characters. We can get more insight than if Roy had narrated his own story and showed us only his take on the people and situations around him.