Two very common differences between many in the yeshiva world and others is (1) wearing tzitzis out and (2) growing peyos behind their ears. Are these two things obligatory or not? I ask b/c I have seen many very choshuv people (even in eretz yisrael) that don’t have peyos and sometimes even a beard and others who also don’t wear their tzitzis out. Are they violating any halachos by not doing these things?
1. There is no obligation to have pe’os behind (or in front) of one’s ears, and the obligation is only that the one should not shave off entirely a patch of hair between the forehead and behind the ears. Some have the custom of leaving long pe’os, others don’t, and there is no obligation or prohibition either way.
2. The same apparently applies to the question of wearing tzitzis in or out. Torah does refer to “seeing and remembering the mitvzos of Hashem,” but the wording clearly refers to the techeles, and Chazal also refer to seeing the techeles and not to the white strings of tzitzis. Therefore, there matter of wearing tzitzis in or out is apparently optional.
However, the Shulchan Aruch writes that one should wear the tzitzis over his other garments so that he can constantly see them and be reminded of the mitzvos (Orach Chaim 8:11), and the Mishnah Berurah (8:26) strongly objected to those who tucked the fringes of their tzitzis into their pants, writing that doing so is a denigration of the mitzvos. He compares the tzitzis to an autographed gift from a king which the recipient would surely want to wear in the most visible manner. This is also ruled by the Shulchan Aruch Ha-Rav (8:18) concerning the fringes themselves.
Yet, the Arizal would wear his tzitzis under his other garments, and latter commentaries (including first and foremost Rabbi Chaim Vital; see Peri Etz Chaim, Tzitzis 1) explain why this is required based on Kaballah. This is the custom of most Sephardi Jews today.
Moreover, there are testimonies of a number of great luminaries who wore their tzitzis tucked in, and Rabbi Gustman zt”l used to say that all the great luminaries of pre-war Vilna used to do so.
Thus, although it has become the general custom of Benei Torah to wear their tzitzis out, this is not a full obligation, and there remain many important Torah scholars, both Sephardi and Ashkenazi, who don’t wear their tzitzis out.