In chapter 28, Scout decides to wear her costume on the way home. How does this help her understand what happens on the way home?

Because the ham costume's skeletal structure is made out of chicken wire, this actually protects Scout from being easily picked up or hurt during Bob Ewell's attack. On the other hand, she can't see what is happening around her because the costume gets crushed around and her arms get pinned in the wiring. As a result of the costume restricting Scout's vision and movements, she can't run very well, and she must depend on her other senses to understand what is going on around her. For example, because she forgot her shoes at the school that night, her bare feet help her to feel the cool earth and roots under the tree where the attack happens.

During the attack, Scout can feel when Jem falls on her. She can also feel his hand as he guides her onwards, but she has to listen to find her way. She hears metal scraping on metal, bodies scuffling in the dirt, and other people screaming, moaning, and coughing. In the end, she says, "It was slowly coming to me that there were now four people under the tree" (262). At first, she thinks it is Atticus. It isn't until chapter 29 that Scout puts all the pieces together about what happened as she is retelling it to Sheriff Tate. 

"Then all of a sudden somethin' grabbed me an' mashed my costume. . . think I ducked n the ground. . . heard a tusslin' under the tree sort of. . . they were bammin' against the trunk, sounded like. Jem found me and started pullin' me toward the road. Some--Mr. Ewell yanked him down, I reckon. They tussled some more and then there was this funny noise--Jem hollered. . . an' the next thing--Mr. Ewell was tryin' to squeeze me to death, I reckon. . . then somebody yanked Mr. Ewell down. . . I thought Atticus had come to help us and had got wore out--" (269-270).

It's at this point that Scout realizes that it was Boo Radley who had saved them that night. With all adults accounted for, and Atticus listening to the story without knowing what happened, she figures out the rest and points to Boo in the corner of the room. Scout has to use deductive reasoning, though to figure out what happened. Without her sight to help her see, she had to listen and piece together the sounds of the commotion around her. 

One piece of evidence found on the costume that Sheriff Tate discovers (that Scout didn't understand at the time of the attack) is a large slice down the fabric of the ham costume. At one point Scout did say that "metal ripped on metal" (262), so that must have been when Mr. Ewell used the kitchen knife to attack her and it scraped the wire rather than slicing her.