The hero is called to adventure when Hagrid brings Harry to Dumbledore. This makes sense to me since when Dumbledore places Harry on the doorstep, he explains to Professor McGonagall about why he is leaving Harry with the Dursleys. He also says the words, " until he is ready" and that, "it's not really good-bye after all". This means that Harry Potter will be seeing Dumbledore someday, and in a sense, that is how Harry is called to adventure. The movie then shows scenes of Harry Potter being maltreated by the Dursleys, which is everyday life to Harry. All the owls dropping in their letters into the house shows an example of how "destiny has summoned the hero".
Joseph Campbell says that the hero may refuse the call to adventure. In this movie, Harry did not refuse but Uncle Vernon and Aunt Petunia both were keeping him from going. Uncle Vernon intercepts all the letters and burns them. He even gets so fanatical over the letters that he nails his mail-flap shut. One day, so many letters fly in through all kinds of openings in the house that Uncle Vernon has had enough and moves in to a shabby, musty and broken-down refuge barely fit enough to be called a home'.
Even so, Uncle Vernon cannot keep Hogwarts from reaching Harry. Harry's magical protector, Hagrid, breaks in to the Dursleys' lodging. Harry finally gets a chance to read his letter while Hagrid argues with the Dursleys. Finally, Harry escapes with Hagrid to Diagon Alley, where he finds out more about his past. I believe that Hagrid is Harry's protector, based on all Hagrid did for him.
I agree with Campbell that the hero must cross the...