[If] one throws a stone into a public domain and kills, he is exiled. R' Eliezer ben Yaakov says: If, after the stone left his hand, the other one put his head out and received the blow, he is exempt. [If] he threw a stone into his own yard and killed —- if the victim had a right to enter there, he is exiled, but if not, he is not exiled; as it is said (Deut. 19:5): And whoever comes with his fellowman into the forest —- [it must be] like the forest, which is a place into which [both] the victim and the assailant have permission to enter. This excludes the courtyard of the householder, into which the victim and the assailant may not [both] enter. Abba Shaul says: [It must be] like chopping wood, [which is] an optional act. This excludes the father who hits his son, and the teacher who chastises his pupil, and the agent of the court.