Q: Two people were running or walking on a sidewalk and accidentally collided, injuring each other and damaging their packages. Are they liable for the mutual damage?

A: Two people who were both walking or both running in public property are liable if they actively injured or damaged each other, but not if they merely collided and were injured or damaged incidentally. According to the Rambam, this means any unintentional damage, but according to Rashi and the Shulchan Aruch, they are liable for any active damaging (such as by swinging an arm or bag) even if unintentional (C.M. 378:7; Gra there).

If one person was running and the other was walking, the person who was running is liable, since he had no permission to run on the sidewalk where people are walking (378:8).

However, if the person was running on Friday afternoon to make arrangements for Shabbos, he is equivalent to the one who was walking, since he is permitted to run then. Thus, he would also be exempt if the two merely collided. The same is true regarding someone who was running to save another person’s life (see Aruch Hashulchan 378:119; Pischei Choshen, Nezikin 1:[72].)