Remember that "omniscient" means all-knowing, in other words, someone that knows everything that happens at all times, something like a god. The narrator is the one that tells the story, so an omniscient narrator tells us the story with the knowledge of everything that happens in it. We can know the character's feelings, thoughts, and actions through it. This type of narrator limits itself to tell the story without forming part of it, the characters are not aware of it's existence.
In this excerpt it is useful as we can see the point of view of the mother, Beatrice, that is worried for her son; as well as the point of view of the coach and his commitment. We can understand in a better way why things happened the way they did.