How many for Chazaras Hashatz?

Question: How many people need to have finished davening shemone esrei before the chazan can continue?

Answer: The Shulchan Aruch (OC 124:4) writes that the chazan should wait for nine others to respond before beginning chazaras hashatz. Failing that, it is close to making a beracha l’vatala. Elsewhere, the Shulchan Aruch (OC 55:6) seems to contradict himself, however, by saying that if one of the ten cannot respond as they have begun davening or fallen asleep, they may still be included. The acharonim give different solutions to explain the difference. The Magen Avraham (55:8) concludes that one does not need nine to answer for chazaras hashatz (See Taz, Pri Chadash and Aruch Hashulchan OC 55:13), while the Shulchan Aruch Harav (OC 55:7), Kitzur Shulchan Aruch (20:2) and Kaf Hachaim (OC 55:48; 124:20) maintain that there does need to be a minyan.

R’ Ephraim Greenblatt (Rivevos Ephraim 3:145) explains that one only needs a minyan when repeating chazaras hashatz. It is sufficient to have just six men to say kaddish during maariv, and one can rely on others still davening or sleeping.

The Noda Biyehuda (EH 1:54) was asked about someone who was mesader kiddushin without checking that there was a minyan present for the berachos. He replied that while lechatchila one needs to have a minyan present for all devarim shebikedusha, bedieved if one does not have a minyan, one is still yotzei. He quotes the Gemara Yerushalmi (Megilla 30b) to prove his point: If people leave the davening in the middle, leaving less than a minyan, the chazan may continue.

R’ Shmuel Wosner (Shevet Halevi 4:14) however, challenges this proof, differentiating between starting chazaras hashatz when you need a minyan to bring the shechina, and already having a minyan, when the shechina will not leave just because one or two people do.

In conclusion, one should ideally wait for nine others to respond for chazaras hashatz, though can rely on the more lenient authorities when absolutely necessary (Tzitz Eliezer 12:9; Yalkut Yosef 124:14). One can say kaddish after maariv with only six men who have finished their amida.