What is one to do if he missed hearing a word in Kerias Hatorah?
*This Halacha deals specifically with the case that the Baal Korei read all the words of the reading but simply an individual member of the congregation did not hear a word or words from the reading due to noise or other distraction of the like. If, however, the Baal Korei himself missed the reading of a word, then the law is more stringent as explained below in A and in our corresponding Sefer “The Laws of Kerias Hatorah” Chapter 10 Halacha 2-see there for the full details of this subject!
Is Kerias Hatorah an obligation of the individual or of the congregation: It is debated amongst the Poskim if Kerias Hatorah is an obligation upon the congregation or is a personal obligation upon each individual. Some Poskim rule that it is an obligation upon each individual to hear the Torah reading. However, majority of Poskim rule that it is a general obligation upon the congregation and not upon the individual. [According to this latter approach, one may live in a city that does not have a Minyan, even though he will miss Kerias Hatorah.] Practically, however, even according to the latter approach, every man is initially required to place effort to be present by the Torah reading, and create a community Minyan, similar to the obligation one has to make a Minyan for Davening. Likewise, every man who is present by the Minyan is obligated to hear every single word of the reading.
The law if the Baal Korei Skipped a word: If the Baal Korei skipped [a verse or] even one word, or even one letter, in the Shabbos Torah reading of Shacharis he is required to go back and read the verse that contains the skipped part. By readings of other days, if one of the Aliyos did not read three whole verses as a result of the skipped word/letter/verse, then that Aliya must be repeated in all cases.
According to the first opinion brought above, an individual who missed even one word of Kerias Hatorah on Shabbos by Shacharis, or by other readings if this caused him to not hear three full verses by each Aliyah, does not fulfill his obligation and must [thus join another Minyan to make up the reading of the verse that contained the missed word, or] if there is a Minyan of men who missed the same word, then they are to make a Minyan to read the area that was missed, with a Bracha. However, according to the second, majority, opinion brought above, even one who missed the entire Torah reading of his Minyan, and certainly if he only missed a few words, is not obligated to make it up by another Minyan, and so is the final ruling. Even if a group of ten people in the Shul could not hear some of the words, nevertheless, they are not to have the Sefer Torah read again with an Aliyah to make up the missed words, and it is even forbidden to do so. [However, one is to read the missed areas to himself from a Chumash. Furthermore, some are scrupulous if they miss a word to join the Minyan of another reading. This, however, is only applicable to be done when a word was missed from a weekly Parsha Shabbos reading, and not by other times of Kerias Hatorah, unless he did not hear three full verses by each Aliyah.] The above is only regarding the law Bedieved if one already missed a word in Keiras Hatorah, however, initially according to all opinions every man who is present by the Minyan is obligated to hear every single word of the reading and it is a grave sin to talk or perform other distracting activities during the reading.
One who did not hear all the words from the Baal Korei is nevertheless not required to make up the reading by another Minyan. However, one is to read the missed areas to himself from a Chumash. Furthermore, some are scrupulous if they miss a word to join the Minyan of another reading.
 See Piskeiy Teshuvos 135:2; 282:2; Igros Kodesh 9:79, printed in Shulchan Menachem 2:166
 Implication of Raavan 73 who rules that one needs Kavana to be Yotzei the blessings; Shelah in Hagahos Yeish Nochlin “If one did not hear even one word he is not Yotzei the reading at all”; Birchas Shmuel Yevamos 21 in name of Rav Chaim of Brisk; Biur Halacha 146:2 “Viyeish Matririn” that the obligation of Ezra is on each individual [however see Biur Halacha 135:14 “Ein Mevin” “There is no obligation on the individual”]; Igros Moshe 4:40; See Admur 282:5 “And all the congregation fulfill their obligation through hearing him,” hence implying that there is an obligation upon the individual [at least when he is present by the Minyan. Vetzaruch Iyun![; See Tikkunei Zohar Tikkun 21 p. 63a “This is why the Sages established to hear the Torah during prayer, in order so it be a complete Karban for man.” See Igros Kodesh ibid that there are two types of Kerias Hatorah, one being a community obligation and the second being a personal obligation; See Likkutei Sichos 4:1283; Pardes Chabad 7:100; Hearos Veiyunim Kfar Chabad 5:132
 Implication of Tosafos Sukkah 52a; Ramban Milchamos Hashem Megillah 5a “All that which we were taught in the Mishneh is an obligation on the congregation and not on the individual”; Ran Megillah 3a in name of Ramban ibid and implication of Ran 13b; Radbaz 1:572; Noda Beyehuda Tinyana 15; Tzemach Tzedek 35-7 “The obligation is not on the actual congregation for them to hear all seven Aliyos, and rather it suffices for there to be seven readers, and it is not similar to Kerias Megillah which is an obligation on each individual to hear the entire Megillah”; Tzemach Tzedek Megillah 3:6-3; Peulas Sachir on Maaseh Rav 175 in name of Gr”a; Semicha Lechaim of Rav Chaim Falagi; Maharshag 2:92; Mishneh Sachir 1:88; Aruch Hashulchan 69:14; Imrei Yosher 2:171; Biur Halacha 135:14 “Ein Mevin” “There is no obligation on the individual” [however see Biur Halacha 146:2 “Viyeish Matririn” that the obligation of Ezra is on each individual]; Tziyunim Letorah Klal 9 in length; Har Tzevi 1:58; Minchas Shlomo 2:4-14; Yabia Omer 7:9; 8:17; Teshuvos Vehanhagos 1:148; 3:65; Yagdil Torah 8:15
Must the congregation hear all of the Kerias Hatorah according to this opinion? Some Poskim rule that even the congregation is not obligated to hear the entire Kerias Hatorah during the reading, so long as they hear most of it, and it was all read. Accordingly, even a Katan may read one of the Aliyos. [Tzemach Tzedek ibid] Other Poskim, however, rule that the entire congregation must hear the entire reading to fulfill their obligation, and hence a Katan is invalid to read any Aliyah. [Admur 282:5; M”A 282:6]
 Maharshag 2:92
 See Tzafnas Paneiach on Rambam Tefilla 12:5 based on Moed Katan 23a that even according to Ramban ibid, one has an obligation to create a Minyan if there is none in his area; See Ashel Avraham Butchach Tinyana 90 that it is similar to the obligation to Daven with a Minyan; See Likkutei Sichos ibid
 Admur 284:11 “It is an obligation upon all to hear the Haftorah just as is regarding the Parsha in the Sefer Torah”; Beis Yosef 146; Rabbeinu Yerucham 2:3 in name of Maharam; Piskeiy Teshuvos ibid footnote 14; 137:3; 282:2; See Chapter 8 Halacha 3 regarding the prohibition to talk during Kerias Hatorah and how each person is to pay attention to the reading
 Admur 282:20; Michaber 137:3; 282:7; Hagahos Maimanis Tefilla 12 Mem; Miseches Sofrim 11:6; Ketzos Hashulchan 84:10; Piskeiy Teshuvos 137:1-2; 282:11
 M”B 137:5 as brought in Michaber 137:5; Piskeiy Teshuvos 137:1
 See Shelah in Hagahos Yeish Nochlin “If one did not hear even one word he is not Yotzei the reading at all”
 Igros Moshe 4:23; 40
 See Tzemach Tzedek 35-7 and all Poskim above who rule that the obligation is on the congregation and not on the individual; See Maharshag 2:92: Mishneh Sachir 1:88; Minchas Shlomo 2:4-15; Tzitz Eliezer 18:5; Teshuvos Vehanhagos 1:148; 3:65; Piskeiy Teshuvos 135:2 footnote 15; 137:3
 See Mishneh Sachir ibid; Piskeiy Teshuvos ibid
 See P”M 143 A”A 2; Rav Poalim 1:52; Ketzos Hashulchan 25:14; Maaseh Rav 129; Koveitz Hisachdus that so did Maharitz Dushinsky; Mishmeres Shalom Koidenov 13:2; See Piskeiy Teshuvos 135 footnote 14; 143:5; See Piskeiy Teshuvos 135 footnote 14
The reason: As the custom is to finish the entire Torah annually, aside for the obligation of Shnayim Mikra.
 Igros Moshe 4:23; 40 that it is proper to do so
 Igros Moshe ibid