According to the halakha, the public domain is available to all people for normal use. Thus a person can walk freely in the public thoroughfare, and if he and another pedestrian bump into one another, neither will have to pay the other for any damage or injury, since they were both walking in an accepted manner. This is true with regard to walking – will it be true if the person was running, as well?
According to Isi ben Yehuda running is not considered a normal activity, which is why someone who runs and causes damage or injury will be considered to be at fault and will be responsible to pay damages. One exception is on Friday afternoon before Shabbat, when running in public is considered normal behavior.
The Tosafot Yom Tov brings two approaches to explaining Isi ben Yehuda’s position. One approach is to permit running on erev only if the person is involved in the mitzva of Shabbat preparation. If, however, the person was running to deal with some personal issue, then he would still be held responsible for any damage that he causes. Another approach is to say that since it is commonplace for people to be running on Friday afternoon, that is considered normal behavior, and therefore someone who does damage while running will not be held responsible.
What might be the purpose of running on erev in the late afternoon? The Gemara points to the practice of some of the Sages who would go out into the fields to welcome the Sabbath – a tradition that has played a role in the development of the Kabbalat service that is customary in synagogues to this day –
Rabbi Hanina would say, “Come, let us go out to greet Shabbat Kallah Malketa – the Sabbath Queen.”
Rabbi Yannai would say, “Bo’ee kallah, bo’ee kallah – welcome the Sabbath as a bride.”
The Maharsha points out a difference between the behavior of these two sages. Rabbi Hanina treated the Shabbat like a queen, and as a subject of the monarch he went out to greet her, while Rabbi Yannai acted in the role of the bridegroom who stood in place welcoming his bride. It should be noted that there is a striking difference between the awe and seriousness that is involved with welcoming the king as opposed to the joy and celebration that takes place at a wedding feast.