Mishnah 5 in chapter 3 of tractate Bava Kamma continues to deal with people who inadvertently cause damage in the public domain. However, here they function as an "adam hamazik" (a person who damages) - as someone who causes the damage with his body, as opposed to a situation where they act as an inanimate pit that causes damage. In all these cases, and indeed throughout the entire tractate, the first question to ask regarding the damager is: Did he act irresponsibly? If he acted responsibly, he will be exempt by law; if he acted irresponsibly, he will be liable. This is the rule that runs like a common thread throughout the tractate, and nowhere is it expressed more clearly than in this Mishnah.
Two people walking toward each other:
"Zeh ba bechavito vezeh ba bekorato, nishberah kado shel zeh bekorato shel zeh - patur, shelazeh reshut lehalech velazeh reshut lehalech" - Two people are walking in the public domain toward each other. One is carrying his barrel, an earthenware vessel made of fragile material, and the other is carrying his wooden beam. The earthenware vessel shatters against the beam, and the person carrying the beam is exempt from paying.
The reason for this: Each of them is granted the right to walk in the public domain in his usual manner, and each one is responsible to watch out for himself. The owner of the beam collided with the owner of the barrel exactly as the owner of the barrel collided with the owner of the beam. The act was not done intentionally, and since neither of them acted irresponsibly, negligently, or in an unusual manner, the finger of blame is pointed at the owner of the beam no more than it is pointed at the owner of the barrel.
If the owner of the beam was first and the owner of the barrel was last:
The Mishnah moves on to a case where the two are walking in the same direction, with the beam carrier in front and the barrel carrier behind him. We have three situations before us:
"Nishberah chavit bekora - patur ba'al hakora" - The person walking behind hurried too much and collided with the one walking in front of him. The owner of the beam is exempt, as he did nothing wrong: he was simply walking in the public domain and carrying his beam in his usual manner, and it was the second person who collided with him from behind and broke his vessel.
"Ve'im amad ba'al hakora - chayav" - If the owner of the beam suddenly stopped in the middle of the public domain to rest, he acted improperly. The public domain is a place for walking, not standing, and people do not expect a person to stop there; one who wants to rest should step to the side of the road. Since he acted irresponsibly, he is liable to pay for the damages to the barrel. This liability is not based on the laws of a pit - since one is exempt for damage to vessels in a pit - but rather on the laws of a person who damages, a person who irresponsibly stood with a large beam in his hand and shattered vessels with it.
"Ve'im amar leba'al hachavit amod - patur" - If he warned the person walking behind him and informed him that he was stopping, he is exempt. He did not act irresponsibly but rather did everything in his power: he needed to rest for a moment and alerted the one walking behind him. From then on, the responsibility lies with the second person.
If the owner of the barrel was first and the owner of the beam was last:
Now the order is reversed: the barrel carrier is walking in front and the beam carrier is behind him. Correspondingly, there are three situations:
"Nishberah chavit bekora - chayav" - The owner of the beam in the back hurried and collided with the one walking in front of him. It is his responsibility to watch where he is going; he is permitted to walk in the public domain, but he has no right to collide with people from behind, and therefore he bears responsibility for the damage.
"Ve'im amad ba'al hachavit - patur" - If the barrel carrier suddenly stopped, he acted improperly. One does not stop in the public domain, as people expect a walker to continue on his way. Shifting the position of the load on one's shoulder is not considered stopping, but stopping to rest belongs on the side of the road. Since he is the one who caused the mishap, the person walking behind him is exempt.
"Ve'im amar leba'al hakora amod - chayav" - If the barrel carrier alerted the person walking behind him and asked him to stop, and that person did not stop but continued and collided with him, shattering the barrel with his beam, he is liable, as he acted irresponsibly: he should have stopped and did not.
"Vechen zeh ba benero vezeh bepishtano":
These exact same principles also apply when, instead of beams and barrels, one carries an open flame of a lamp and the other flax, which is a highly flammable material. Although flax is sensitive to fire and fire is more dangerous than a beam, the rules are the same in both cases: a person is allowed to carry his fire or his beam in the marketplace, provided that he acts responsibly like any other person. If he violates the rules of responsible and expected behavior, he is liable; if he maintains them, he is exempt.
Therefore, if a person runs in the street with a beam in his hand, he is liable even if the two collided head-on, because he has no right to run in the public domain with a beam in his hand. The same applies to one who runs in the street with fire: if the fire catches onto his fellow - he is liable, because he has no right to run around in this manner.
In summary: In this Mishnah, the liability of the damager is measured by a single standard - whether he acted responsibly. Two people walking toward each other, both of whom have the right to walk, are exempt. When two people walk one behind the other, the responsibility falls on the one who deviated from expected behavior: the one walking behind who collided with his fellow, or the one walking in front who stopped without warning. If he warned his fellow - he is exempt, and if he did not warn him - he is liable. The same applies to the candle and the flax, as well as to one who runs in the public domain, which he has no right to do.