The holiday of Lag BaOmer is associated with having haircuts. This source sheet looks at the reasons behind that.
(א) נוֹהֲגִים שֶׁלֹּא לִשָּׂא אִשָּׁה בֵּין פֶּסַח לַעֲצֶרֶת עַד ל''ג לָעֹמֶר, מִפְּנֵי שֶׁבְּאוֹתוֹ זְמַן מֵתוּ תַּלְמִידֵי רַבִּי עֲקִיבָא; אֲבָל לְאָרֵס וּלְקַדֵּשׁ, שַׁפִּיר דָּמִי, וְנִשּׂוּאִין נָמֵי, מִי שֶׁקָּפַץ וְכָנַס אֵין עוֹנְשִׁין אוֹתוֹ. הַגָּה: מִיהוּ מִלַּ''ג בָּעֹמֶר וָאֵילָךְ הַכֹּל שָׁרֵי (אַבּוּדַרְהַם וּבֵית יוֹסֵף וּמִנְהָגִים).
(ב) נוֹהֲגִים שֶׁלֹּא לְהִסְתַּפֵּר עַד ל''ג לָעֹמֶר, שֶׁאוֹמְרִים שֶׁאָז פָּסְקוּ מִלָּמוּת.
(1) It is customary not to get married between Pesach and Shavuot, until Lag BaOmer (the 33rd day), because during that time, the students of Rabbi Akiva died. However, to do "erusin" and "kiddushin" (engagement and betrothal) is OK. And even for "nisuin" (marriage), if someone did so, we do not punish him. Rema: however, from Lag Ba'Omer onwards, all this is permitted (Abudraham, Beit Yosef & Minhagim).
(2) It is customary not to cut one's hair until Lag BaOmer, since it is said that that is when they stopped dying.
Orach Chayim - the laws about Jewish time (prayer time and holidays)
Yoreh De’ah - the laws about Jewish living (kashrut, conversion, mourning, Israel)
Even Ha’ezer - the laws about getting married and divorced
Choshen Mishpat - the laws about business, money, and courts
This is in the part of Orach Chayim about Pesach.
What questions does this raise for you?
רַבִּי עֲקִיבָא אוֹמֵר: לָמַד תּוֹרָה בְּיַלְדוּתוֹ — יִלְמוֹד תּוֹרָה בְּזִקְנוּתוֹ. הָיוּ לוֹ תַּלְמִידִים בְּיַלְדוּתוֹ — יִהְיוּ לוֹ תַּלְמִידִים בְּזִקְנוּתוֹ, שֶׁנֶּאֱמַר: ״בַּבֹּקֶר זְרַע אֶת זַרְעֶךָ וְגוֹ׳״. אָמְרוּ: שְׁנֵים עָשָׂר אָלֶף זוּגִים תַּלְמִידִים הָיוּ לוֹ לְרַבִּי עֲקִיבָא מִגְּבָת עַד אַנְטִיפְרַס, וְכוּלָּן מֵתוּ בְּפֶרֶק אֶחָד, מִפְּנֵי שֶׁלֹּא נָהֲגוּ כָּבוֹד זֶה לָזֶה. וְהָיָה הָעוֹלָם שָׁמֵם, עַד שֶׁבָּא רַבִּי עֲקִיבָא אֵצֶל רַבּוֹתֵינוּ שֶׁבַּדָּרוֹם וּשְׁנָאָהּ לָהֶם: רַבִּי מֵאִיר, וְרַבִּי יְהוּדָה, וְרַבִּי יוֹסֵי, וְרַבִּי שִׁמְעוֹן, וְרַבִּי אֶלְעָזָר בֶּן שַׁמּוּעַ, וְהֵם הֵם הֶעֱמִידוּ תּוֹרָה אוֹתָהּ שָׁעָה. תָּנָא, כּוּלָּם מֵתוּ מִפֶּסַח וְעַד עֲצֶרֶת. אָמַר רַב חָמָא בַּר אַבָּא וְאִיתֵּימָא רַבִּי חִיָּיא בַּר אָבִין: כּוּלָּם מֵתוּ מִיתָה רָעָה. מַאי הִיא? אָמַר רַב נַחְמָן: אַסְכָּרָה.
Rabbi Akiva says that the verse should be understood as follows: If one studied Torah in his youth he should study more Torah in his old age; if he had students in his youth he should have additional students in his old age, as it is stated: “In the morning sow your seed, etc.”
They said by way of example that Rabbi Akiva had twelve thousand pairs of students in an area of land that stretched from Gevat to Antipatris in Judea, and they all died in one period of time, because they did not treat each other with respect.
And the world was desolate of Torah until Rabbi Akiva came to our Rabbis in the South and taught his Torah to them. This second group of disciples consisted of Rabbi Meir, Rabbi Yehuda, Rabbi Yosei, Rabbi Shimon bar Yochai, and Rabbi Elazar ben Shamua. And these are the very ones who upheld the study of Torah at that time. Although Rabbi Akiva’s earlier students did not survive, his later disciples were able to transmit the Torah to future generations.
With regard to the twelve thousand pairs of Rabbi Akiva’s students, the Gemara adds: It is taught that all of them died in the period from Passover until Shavuot. Rav Ḥama bar Abba said, and some say it was Rabbi Ḥiyya bar Avin: They all died a bad death. The Gemara inquires: What is it that is called a bad death? Rav Naḥman said: Diphtheria.
What happens in this text?
תַּנֵּי רִבִּי שִׁמְעוֹן בֶּן יוֹחַי. עֲקִיבָה רִבִּי הָיָה דוֹרֵשׁ דָּרַ֨ךְ כּוֹכָ֝ב מִֽיַּֽעֲקֹ֗ב. דָּרַךְ כּוֹזִבָּא מִיַּעֲקֹב. רִבִּי עֲקִיבָה כַּד הֲוָה חֲמִי בַּר כּוֹזִבָּה הֲוָה אֲמַר. דֵּין הוּא מַלְכָּא מְשִׁיחָא. אָמַר לֵיהּ רִבִּי יוֹחָנָן בַּר תּוֹרְתָא. עֲקִיבָה. יַעֲלוּ עֲשָׂבִים בִּלְחָיֵיךָ (וְאַדַּיִין) [וְעַדַּיִין] בֶּן דָּוִד [לֹא] יָבֹא.
Rebbi Shimon ben Yochai stated: Akiba my teacher used to preach, there appeared a star out of Jacob there appeared Koziba out of Jacob. When Rebbi Akiba saw Bar Koziba he said, “this is King Messiah”. Rebbi Yochanan ben Torta said to him, “Akiba! Grass will grow from your jaws and still David’s son (still has to) [will not have] come.”
Given how Rabbi Akiba felt about Bar-Kochba, and given that the Talmud sometimes speaks cryptically, how might his students have died?
(ט) ומסר ר' עקיבא את עצמו [להריגה] אחר שנפטר ר' יוסי בן קיסמא. ונהרג ר' חנינא בן תרדיון ונתמעטה החכמה [אחריהם]. והעמיד [רבי עקיבא] תלמידים הרבה והוה שמדא על התלמידים של ר' עקיבא ...
R' Akiva gave himself over to execution after R' Yosi ben Kisma died. R' Chanina ben Tradiyon was also killed and wisdom diminished after they passed. R' Akiva raised up many students, but a religious persecution waged against his students...
What does Rav Sherira Gaon’s explanation for the demise of Rabbi Akiba’s students support in our understanding of why they might have died?
אמרו על ר' עקיבא ששנים עשר אלף זוגות תלמידים היו לו וכלן מתו בפרק אחד על שלא נהגו כבוד זה לזה והיה העולם שמם בלא תורה עד שבא לו אצל רבותינו שבדרום ושנה להם לר' מאיר ור' שמעון ור' יהודה ור' יוסי ור' אלעזר בן שמוע והם הם העמידו את השעה ותלמידים אלו הוזכר כאן שכלם מתו מפסח ועד עצרת וקבלה ביד הגאונים שביום ל"ג בעומר פסקה המיתה ונוהגים מתוך כך שלא להתענות בו וכן נוהגים מתוך כך שלא לישא אשה מפסח עד אותו זמן:
Meiri, Tractate Yevamot 62b
There is a received tradition from the Geonim that on the 33rd day of the Omer, the deaths (of the students of R. Akivah) stopped...and we also have the custom not to get married from Pesach until this time
Other possible explanations for why Lag BaOmer became a day of celebration include that there was a lull in the fighting during the Bar-Kochba rebellion, or that possibly they captured Jerusalem on this day in 132 CE, or that Rabbi Akiba “ordained” the 5 rabbis on Lag BaOmer, thus ensuring that Jewish tradition would continue to be taught. Additionally, the Byzantine Emperor Julian tried to rebuild the Third Temple, but an earthquake in 363 CE stopped him and that supposedly happened on this day.
Which explanation resonates with you the most?

