In chapter 16 of Hoot, when Roy and his parents take their day trip to the Everglades, Beatrice Leep sneaks into their home and hides under Roy's bed. She gets in by pulling the sliding glass door off its track from the porch outside. Roy doesn't know she's there until he has gone to bed for the night and hears someone calling his name from under his mattress. 

At first he's upset that she would break into their home, but when she tells him why she's there, he calms down and offers her refuge for the night. She explains that "things got kinda hairy at home." Her father and step-mother had a bad fight and threw things at each other. Although Beatrice is a tough kid, not easily frightened, Roy can tell she's shaken up by witnessing domestic violence. She didn't know where else to go, so she went to Roy's house and hid.

Roy feels bad that he lost his temper at her. Since his mother and father are loving and nurturing, he finds it hard to imagine living with parents who could behave so erratically.

Why does Beatrice break into Roy's house in "Hoot"?

Beatrice breaks into Roy's house because "things got kinda hairy at home (and she) didn't know where else to go".

After he has gone to bed, Roy is surprised to hear his name being whispered in his room.  Beatrice slides out from underneath his bed, and when Roy, stunned, asks how she got in the house, she replies matter-of-factly, I didn't bust any windows or anything...the sliding door on your porch popped right off the track...they all do". 

Beatrice explains that her parents, who are bizarre and dysfunctional even under the best of conditions, "got in a huge fight".  Her mother threw a clock radio at (her father's) head, so he beaned her with a mango."  Roy, who "had always thought that Beatrice Leep wasn't afraid of anything", feels bad that she has to live "in a house where the grownups (behave) so idiotically", and tells Beatrice that she can stay the night as long as his parents don't find out.  He chivalrously offers to sleep on the floor so she can have the bed, but she refuses, so Roy gives Beatrice "a pillow and a blanket, and she stretch(es) out happily on the carpet" (Chapter 16).