Can someone charged with watching an object pass it on to a third party who agrees to watch it?
We learned previously, (Massekhet Bava Kamma 11b) that there is a disagreement with regard to this question. According to Ulla in the name of Rabbi Elazar, shomer she-masar le-shomer – when one person who was watching an object passes it on to another person – he will not be responsible for anything beyond his original obligation. Since he gave it to another responsible individual, he has not done anything wrong. According to this opinion, this is true not only in a case where a shomer hinam (someone who volunteered to guard the object) raised the level of shemira by giving it to a shomer sakhar (someone who was paid to watch the object), but also if a shomer sakhar lowered the level of shemira by transferring it to a shomer hinam. Rava disagrees, ruling that a shomer she-masar le-shomer will be responsible for everything that takes place – even if a shomer hinam raised the level of the shemira by transferring it to a shomer sakhar. This is because the owner can say to the guard – “I trust you when you take an oath; I do not trust the man who you gave it to.”
As understood by the Gemara on our daf, our Mishna (55b) teaches that when a shomer transfers the animal to a ro’eh – a shepherd – the ro’eh becomes fully responsible for any damage that the animal does. This stands in apparent contradiction to Rava’s position that a shomer she-masar le-shomer will always be responsible.
Rava explains that our Mishna is talking about a specific case, when the original shomer has given the animal to his assistant to watch. The Rashba explains that since it is understood that the primary shepherd cannot take care of all the animals all of the time, it is clearly understood that he will hire assistants to help him. Thus, this is not a typical case of shomer she-masar le-shomer.