Gemara

(Beraisa #1): If Pesach was slaughtered Lo l'Ochlav and Zerikah was done Lo l'Ochlav, it is Kosher and one is Yotzei with it.

Suggestion: This is like R. Noson, and unlike Chachamim.

Rejection: It is even like Chachamim. Intent for who will eat it does not affect Zerikah. ("Ish l'Fi Ochlo" discusses Shechitah.)

(Beraisa #2): If Pesach was slaughtered b'Taharah and then the owners became Tamei, we are Zorek b'Taharah. The owners may not eat it b'Tum'ah.

(R. Elazar): This is only like R. Noson.

(R. Yochanan): It is even like Chachamim. The case is, most of the Tzibur became Tamei. They bring Pesach b'Tum'ah.

Question: If so, they may eat the meat b'Tum'ah!

Answer: This is a decree, lest the owners become Tamei next year after Zerikah, and they will think that they may eat, just like they ate the previous year even though they became Tamei;

They will not realize that they were permitted only because they were Tamei at the time of Zerikah, but one who was Tahor at the time of Zerikah may not eat b'Tum'ah.

Yerushalmi (7:5, based on the text of Or Some'ach) (R. La citing R. Yochanan): Beraisa #2 is like R. Noson, who says that one is Yotzei with Zerikah without Achilah. (Rabanan hold that if the owners became Tamei before Zerikah, they are detained to Pesach Sheni.)

(Continuation of Beraisa #2): If it was slaughtered b'Taharah and the blood and Tzibur became Tamei, they do Zerikah b'Tum'ah, but it is not eaten b'Tum'ah.

(R. Yirmeyah citing R. Yochanan): This is due to Mar'is ha'Ayin, lest people say that they saw Pesach eaten b'Tum'ah.

Question: If so, we should not do Zerikah b'Tum'ah, lest people say [that they saw [Shechitas] Pesach b'Taharah and Zerikah b'Tum'ah!

Answer: We must say that the Beraisa is like R. Noson.

R. Noson agrees about a Choleh or Zaken (sick or old person).

Rishonim

Rambam (Hilchos Korban Pesach 7:8): If Pesach is offered b'Tum'ah, it is eaten b'Tum'ah. This is when the Tzibur became Tamei before Zerikah, but not if they became Tamei after Zerikah.

Rambam (9): If Pesach was slaughtered b'Taharah and most of the Tzibur became Tamei before Zerikah, we are Zorek and the Pesach is not eaten. This is a decree, lest another year they become Tamei after Zerikah and eat it b'Tum'ah.

Kesef Mishneh: The Rambam contradicts what he wrote in Halachah 8, that if the Tzibur became Tamei before Zerikah, it is eaten b'Tum'ah! I answer that Beraisa #2 taught that if Pesach was slaughtered b'Taharah and then the owners became Tamei, we are Zorek b'Taharah, but it is not eaten b'Tum'ah. The Gemara concluded that this is a decree, lest the owners become Tamei [after Zerikah] and think that they may eat, just like the previous year. In Halachah 8 the Rambam taught letter of the law, and here he teaches the decree.

Tosfos (78b DH Leima): How could we think that Beraisa #1 is like R. Noson? R. Noson and Rabanan argue only about the meat, but all agree that the person must be Chazi (potentially able) to eat! Also, if so (it is like R. Noson, and he does not require that one is Chazi to eat), even if it was slaughtered Lo l'Ochlav, he should be Yotzei! Why does it say that it was slaughtered l'Ochlav? Also, how could we think that intent for who will eat applies to Zerikah? The entire Gemara holds that that intent for eaters does not apply to Zerikah! The Ri answers that "Zerikah was done Lo l'Ochlav" does not mean that Zerikah was done not for those who will eat it. Rather, at the time of Zerikah the owners were sick. We suggested that this is like R. Noson. Since he is so lenient and does not require meat that may be eaten, [perhaps] he is not concerned if at the time of Zerikah the owners were not Chazi to eat. Rabanan, who are stringent and require meat that may be eaten, likewise require owners who at the time of Zerikah are Chazi to eat. R. Elazar holds like this, that R. Noson requires only that at the time of Shechitah the owners were Chazi to eat.

Or Some'ach: In the Yerushalmi, R. Yochanan establishes Beraisa #2 like R. Elazar does in the Bavli. We establish the Beraisa like R. Noson, who holds that Achilas Pesach is not Me'akev. One is Yotzei through Zerikah without Achilah. Therefore, even if the Tzibur became Tamei before Zerikah, it is not eaten b'Tum'ah. He does not say "it was brought only for Achilah." According to Rabanan, if it will not be eaten, we would not do Zerikah. A Tzibur cannot be detained to Pesach Sheni. Therefore, they offer and eat it b'Tum'ah. R. Noson agrees about a Choleh or Zaken, i.e. even though he is Choleh at the time of Zerikah, we are not Zorek for him, for he cannot eat. He argues only about a Tamei, since one who was Tamei from the beginning may even eat with a [Tamei] Tzibur. Therefore, he is considered Chazi to eat. In the Bavli, R. Elazar explains R. Noson like this, and R. Yochanan did not disagree. If there is not a k'Zayis for someone, Pesach is not proper for Achilah. This is not Me'akev according to R. Noson. If the owners became Tamei and the blood and Kohen are Tehorim, if the owners were Temei'im at the time of Shechitah, the Torah detained them. If the owners were Tehorim at the time of Shechitah and Temei'im at the time of Zerikah, we are Zorek for them, and it is not eaten b'Tum'ah. If one is Choleh at the time of Zerikah, we are not Zorek for him, for he is not Chazi to eat. We must say that this Sugya in the Bavli and Yerushalmi holds that a Tamei Mes may send Korbanos [through a Shali'ach]. The Rambam (6:2) holds that even a Tevul Yom of Mes may not send Korbanos, even though he could eat them at night. If so, why does it help to establish the Beraisa like R. Noson? Why are we Zorek for a Tamei Mes? Even though R. Noson does not require being Chazi to eat, he is not better than a Tamei Mes on the seventh day! In the Bavli, R. Elazar established the Beraisa like R. Noson. In the Yerushalmi, R. Elazar holds that we do Shechitah and Zerikah for a Tamei Mes on the seventh day, since he can eat at night. We could say that the Beraisa discusses Tum'os of Mes that do not interrupt Nezirus. (For such Tum'os, we do Shechitah and Zerikah on his seventh day.) However, if so, this is even if he was Tamei at the time of Shechitah!

Or Some'ach: The Yerushalmi (8:8) says that if an individual became Safek Tamei in a Reshus ha'Yachid, R. Hoshaya says that he is detained to Pesach Sheni, and R. Yochanan says that we send him far from the Mikdash. [If we would not send him,] since perhaps he was Tahor, he does not bring Pesach Sheni. He cannot eat due to the Safek. We do not apply "Ish l'Fi Achlo"! He should be detained to Pesach Sheni just like a Choleh or Zaken! Even if Hash-m knows that he was Tahor and permitted to eat, [we did not know, so] he could not eat. If they slaughtered Pesach for him, it was Pasul. R. Yochanan says so in the Yerushalmi, that the Mishnah (9:9) is R. Noson, who holds that one is Yotzei through Zerikah without Achilah. This is unlike Tosfos (98b DH Peturim), who distinguishes. Based on what I said, this is good. If a Tzibur became Safek Tamei in Reshus ha'Yachid, they did Pesach and offered it. This is unlike a Choleh, which does not apply to the Tzibur. We consider Temei'im Chazi to eat. R. Noson agrees that if he was Tamei [at the time of Shechitah], he is detained to Pesach Sheni. If he was Tahor, but cannot eat due to Safek, this is like one who owns less than a k'Zayis. Therefore, we send him far away [to enable him to bring Pesach Sheni]. R. Yochanan holds like R. Noson, for several Stam Mishnayos are like him. The Tosefta (7:8; in some editions, 7:12) says that one who was Tahor at the time of Shechitah and Tamei at the time of Zerikah [must do Pesach Sheni] is like Rabanan, and unlike R. Noson. This is why the Gemara brought the Seifa (he was Choleh at the time of Shechitah), but not the case of Tamei [for he is considered Chazi to eat]. According to Tosfos, it is all the same.