What happens in the dark?

They are almost home, near the dark shadow of the tree by the Radleys' house, and are trying to walk faster. It sounds like the person behind them is wearing thick cotton pants. The next time they stop walking, the footsteps behind them suddenly quicken into a run. Jem yells to Scout to run, but her costume throws her off balance. Something is crushed against her and she hears metal ripping. Jem's hand tries to pull her, but she is tangled up in her costume. There is a crunching sound and Jem screams. The man whom they are struggling with grabs Scout and begins to strangle her, when suddenly he is jerked backwards and thrown to the ground. Scout thinks Jem must have saved her, but she still can't see anything. She hears the sound of someone breathing heavily and, walking toward the tree to lean on, reaches out with her toes to find a person on the ground with stubble and the smell of stale whiskey. She makes her way in the direction of the road, and in the streetlight she sees a man carrying Jem, whose arm is hanging down at an odd angle.