After being warned by Atticus about playing the Boo Radley game in Chapter 4, the children attempted to make contact with Boo by placing a note on the end of a fishing pole in Chapter 5. Atticus caught them again, and this time he put his foot down.
"I'm going to tell you something and tell you one time: stop tormenting that man."
Jem and Dill had come up with a new plan in Chapter 6. Under the pretense of going "for a walk" after dark, they took Scout along with them. But
Nobody in Maycomb just went for a walk.
The boys had decided to try and get a peek at Boo through the side window of the Radley house. Slowly and quietly making their way through Boo's back yard, Jem and Scout lifted Dill above the window, but curtains prevented him from seeing anything inside. So Jem decided to try the back porch window. Before he could, however, a shadow emerged, and
... crisp as toast, moved across the porch toward Jem.
But the shadow stopped just short of Jem, then turned around and went back the same way it had come. The children ran for their lives and, in their haste, Jem lost his pants when he became entangled in the Radley's fence.