Jane was locked up in the red room as a punishment for striking John Reed, her degenerate young master. She did not deserve this treatment, because John started the confrontation by mercilessly bullying her, even causing her physical injury when he, unprovoked, threw a book at her head.
Jane, an orphan, is treated as if she is nothing in the home of her aunt and uncle, who have taken her in. Her cousin John Reed "bullie(s) and punishe(s)" her constantly, and he is allowed to do so because Mrs. Reed coddles her son and thinks he can do no wrong. In the situation in question, John calls Jane over to him, and, after spending "some three minutes in thrusting out his tongue at (her) as far as he could without damaging the roots", he strikes her for her purported "impudence in answering mamma a while since...and for (her) sneaking way of getting behind curtains, and for the look (she) had in (her) eyes two minutes since". He then tells her she has no right to take books from the bookshelves to read, since they all belong to him, and orders her to stand by the door. When Jane, having no choice, complies, he flings a book at her, and she falls, striking her head against the door and cutting it. Jane flies back at him in a rage, and for her trouble is accused of attacking "Master John"; she is forcibly removed from the vicinity and carried upstairs to be locked in the "red room" (Chapter 1).