Who takes a stand in chapter 3 of To Kill a Mockingbird, and why?

To Kill a Mockingbird is full of examples of people taking noble stands. One only has to think of Atticus Finch defending Tom Robinson on trumped-up charges of rape and assault. But Scout's beating up Walter Cunningham Jr. in chapter 3 certainly doesn't fall into this category. Scout may be taking a stand of sorts, but there's not much noble about it.

Scout is feeling pretty upset at Walter for the reprimand she received from their novice teacher Miss Caroline. Scout had pointed out to Miss Caroline that she was shaming Walter by lending him a quarter for his lunch, as he wouldn't be able to pay it back. Scout was simply trying to be helpful, but she came across as if she were being impertinent. So Miss Caroline dragged her to her desk, where she gave Scout half a dozen quick whacks with a ruler.

Feeling sore in more ways than one, Scout takes out her anger on Walter by attacking him in the schoolyard. Scout gains a lot of pleasure from rubbing his nose in the dirt. Thankfully, Jem is one hand to pull her off before she can do too much damage. As Jem points out, Scout's bigger than Walter. Even so, Scout's already made her point. She's made a stand of sorts, albeit one that children would be well-advised not to emulate.

In chapter 15 of To Kill a Mockingbird, who takes a stand and why?

In Ch. 15, Atticus takes a stand against what is essentially a lynch mob coming to get Tom Robinson from the Maycomb County Jail.

It all began earlier in the chapter when Sheriff Tate came to the Finch home to warn Atticus that there were men who were angry about him representing Tom. Apparently it was not men from Macomb, but the "Old Sarum bunch", who live in a nearby town. They had been drinking all day and getting angrier and angrier.

Despite the very real threat the men pose, Atticus goes that night to the jail to sit outside and make sure no one hurts Tom. This is at great personal risk to himself, but he feels it is the right thing to do. When the men show up they are angry, probably drunk, and have made sure Sheriff Tate is off on another call so he cannot be anywhere around to help Atticus. The kids then arrive and, by a miracle, Scout manages to diffuse the entire situation by engaging Walter Cunningham's father in conversation about his son. He then directs the mob to leave.

At the end of all of this, Atticus seems incredibly relieved that no harm came to anyone, as was about to be the case. While one could also argue that Scout took a stand in this scenario, she may not have fully understood what it was she was doing. She simply knew she was trying to provide a distraction and that ended up protecting them all, but it was not necessarily an intentional stand. Atticus, on the other hand, knew full well the danger he was facing when he went to the jail and by going to protect Tom, he took a stand against the mob.