Questions: Does the prohibition of “trapping” apply when one catches a young child on Shabbat so that he does not run away or when one grabs a person and puts him in prison on Shabbat? Is it permissible to trap a poisonous snake on Shabbat so that it does not attack people?
Answer: Regarding the question about whether or not trapping applies to human beings on Shabbat, the Sefer “Kovetz” on the Rambam (Hilchot Shabbat Chapter 10, Halacha 22) writes that if one sees a child falling into the river on Shabbat and throws a net into the water to save him has transgressed the prohibition of trapping on Shabbat (unless it is a life-threatening situation in which case it would certainly be permissible, ibid). Similarly, the Responsa Avnei Nezer Chapter 189) writes likewise that trapping does indeed apply to a child.
Nevertheless, the Sefer Chemdat Yisrael (page 61) questions their opinion, for we know that in order to transgress the Torah prohibition of trapping, the creature being trapped must be a kind of creature that is usually trapped, such as birds and fish. Based on this, human beings are not creatures that are usually trapped.
Halachically speaking, Hagaon Harav Shlomo Zalman Auerbach zt”l is quoted in the Sefer Shemirat Shabbat Ke’Hilchata (Chapter 27) as saying that the prohibition of trapping does not apply in these situations at all. If a child is drowning in the river, the prohibition of trapping does not apply when trying to save him. He adds that according to his opinion, even if one sees other animals drowning in the river, there is no prohibition of trapping while trying to save them, for this cannot be considered “trapping” since they will drown in any case if one does not save them. This is similar to catching a dead fish from the sea in which case one certainly has not transgressed the prohibition of trapping on Shabbat.
Similarly, Hagaon Harav Eliezer Yehuda Waldenberg zt”l writes in his Responsa Tzitz Eliezer (Volume 15, Chapter 41) that one may catch a young child running away from his parents, for the nature of a child is to return to his parents and this can be compared to the law of chickens and ducks which we have previously mentioned that since they usually return to their cage/coop on their own, there is no prohibition to trap them.
Maran zt”l in his Chazon Ovadia (Shabbat-Part 5, page 107) quotes their words as Halacha. He adds that the Responsa Shevut Yaakov records an incident that once, a man wanted to leave his wife an Agunah (a woman whose husband leaves her without a divorce essentially still being bound to him) by running away from his city on Shabbat so that the rabbis of the city do not require him to give his wife a Get (bill of divorce). The author of the Shevut Yaakov ruled that this man should be caught and incarcerated on Shabbat. He was not worried about the prohibition of trapping on Shabbat, for we see our Sages were truly concerned about the plight of the Agunah in many cases.
Regarding our second question, poisonous snakes, rabid dogs, or dogs which we suspect may be infected with rabies should be caught or killed even on Shabbat; even if they are not chasing a human being in order to attack him, it is still permissible to kill them, for Shabbat may be desecrated even when there is a doubt about a person’s life being in danger. Similarly, if there is a need to call animal control services to come and kill it, this is likewise permissible on Shabbat.
If it is clear that the snake is not poisonous and its bite will not cause any danger, the Halacha is that if it is chasing a person, one may kill it so that it does not harm the person (since one does not need the snake’s actual body, killing it will not constitute a Torah prohibition and only constitutes a rabbinic prohibition; in such a cause where harm may ensue, our Sages never forbade killing the snake). If the snake is not chasing anyone, it will still be permissible to kill it on Shabbat as long as long as this is being done in a somewhat abnormal fashion, such as, crushing it while one is walking and the like. It is likewise permissible to place a vessel on top of it so that it will not be able to flee until Motza’ei Shabbat (ibid. page 122).