Shmuel and Rav Yochanan's position on how they understand the Mishna implies that if you actually see the vessel, you have to go around it. You can't break it deliberately. But if it's a bor in the middle of the street that can hurt other people, why can't I break it if I can help people from getting hurt?
Soheil Zaman, Sherman Oaks
I assume that this question is on 27b.
I saw that the Mefarshim cite the Me'iri on the Mishnah who says that the person who placed the jug down in the street was tired and wanted to take a breather. It must be that in the short time that he was having a quick rest, somebody came and tripped up on it.
According to this, we can say that one has the right to place down items in Reshus ha'Rabim for a short time if one is tired. The main street is also intended for travelers to take short breaks, within reason. (This is supported by the opinion of Rebbi Yochanan on 20a who says, "It is normal for peole to place their clothing down [in Reshus ha'Rabim] and rest.) One is not allowed to break the property of a traveler behaving in this way (as the Gemara there on 20a says).
Kol Tuv,
Dovid Bloom