Jem sneaks onto the porch of the Radley house in hopes to peek through the window to see Boo. He sees a shadow on the porch wall, and he gets scared and runs. While trying to get over the fence, he snags his pants on a wire. He takes off his pants because he is unable to free himself and runs for home. As he is running, he hears a shotgun blast go off behind him. It is Nathan Radley shooting in the air to make a statement about trespassing on his property. The gossipy, prejudiced Miss Stephanie thinks it was probably a “negro” in the Radley yard.
Jem knows that he will get in trouble with Atticus for snooping around the Radley house. Atticus has already warned Jem to leave the Radleys alone, and Jem and Dill go against his wishes. Deep down, he really doesn’t want to disappoint his father by disobeying him. When Atticus comes out of the house to investigate the gun shot, he sees Jem without any pants on. Dill lies for Jem and says that Jem lost them in a strip poker game.
Later that night, Jem sneaks back to the fence and finds his pants mended and folded neatly where he left them.
Jem deeply respects his father and doesn’t want to disappoint him or get in trouble. He is willing to take the risk and go back to get his pants so his father never finds out about bothering the Radleys. Atticus probably figures it out, but perhaps Atticus feels Jem has been scared enough to warrant any punishment.