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.