Gemara

Suggestion: Perhaps Milah does not override Tzara'as, for an Aseh overrides a Lav alone, but there is also an Aseh not to cut Tzara'as ("v'La'asos k'Chol Asher Yoru Eschem")!

Answer: "Besar" permits even if there is Tzara'as on the Orlah.

133a (Rav Mesharshiya): "Besar" permits a father who intends to cut his son's Tzara'as during circumcision.

Question: If someone else [who is not concerned about the Tzara'as] can circumcise, the father should not be allowed!

Answer: The case is, there is no one else.

Avodah Zarah 27a (Rav): "V'Atah Es Brisi Tishmor" disqualifies a Nochri for circumcision;

(R. Yochanan): We learn from "Himol Yimol." (One who is circumcised may circumcise.)

They argue about a Yisraelis.

Kidushin 29a (Beraisa): "Va'Yamal Avraham Es Yitzchak Beno..." commands a man to circumcise his son.

If the father does not, Beis Din is commanded - "Himol Lachem Kol Zachar."

"Like Hash-m commanded him" exempts women.

Yevamos 40a - Suggestion: Perhaps if the Kohen [who offered a Minchah] wants, he eats it, and if not, another Kohen eats it!

Rejection: "Matzos Te'achel b'Makom Kadosh" - it is a Mitzvah [for him to eat].

Rishonim

Rambam (Hilchos Milah 1:1): The Mitzvah is for a father to circumcise his son. If the father transgressed and did not, he was Mevatel an Aseh, and Beis Din are obligated to circumcise him in the time, and not leave him Arel.

Rosh (Chulin 6:8): A case occurred in which Reuven asked Shimon to circumcise Reuven's son, and Levi circumcised him. Shimon demanded that Levi pay him 10 gold pieces for stealing his Mitzvah, and R. Tam exempted him. Since there is no loss of money, Beis Din does not collect this nowadays. I exempt Levi in any case. Even though Reuven asked Shimon, Shimon did not acquire the Mitzvah to obligate someone else who does it first. This is unlike Kisuy ha'Dam. The Torah said that the one who slaughters [a bird or Chayah], he covers. Likewise, if Reuven wanted to circumcise his son, and Levi did it, Levi must pay. However, if Reuven does not want to do it, all of Yisrael are obligated to circumcise him. Shimon did not acquire the Mitzvah through Reuven's words.

Rosh (Teshuvah 12:3): Even after a son was born, if the father was Makneh with a Kinyan that Shimon will be Ba'al Bris (the Mohel or Sandek), he can retract. This is Kinyan Devarim, which is void (Bava Basra 3a). Rabbeinu Meir says that we follow the custom. Where Situmta (we explain this below) acquires (i.e. people do not retract afterwards), it makes a Kinyan, even though letter of the law, it is not a Kinyan. I question this. Situmta is an action, either marking barrels according to Rashi, or a handshake according to R. Chananel. This is in place of transferring a cloth. Mere words do not acquire. There is no source that this is the custom, and even if it is, we do not follow such inferior customs I fulfill the matter through a handshake, so he will not retract.

Poskim

Rema (YD 264:1): One should seek the best, most virtuous Mohel and Sandek. If one gave it to Ploni, he may not retract. However, if he retracted, it is a retraction. A Kinyan does not help. If he swore, we force him to fulfill it. A woman cannot give to another to circumcise, for she has no connection to the Mitzvah to circumcise her son.

Darchei Moshe (YD 264:1): Or Zaru'a (Hilchos Milah 107) says that if the father knows how to circumcise, he may not let another circumcise. I say that this is like other Mitzvos, in which one may make a Shali'ach in place of himself!

Birkei Yosef (1): This is not difficult. It is a greater Mitzvah to do the Mitzvah oneself (Kidushin 41a)! The Or Zaru'a and Maharam Rikanti 592 say 'one may not let another circumcise', i.e. he himself did not do the Mitzvah incumbent on him.

Ketzos ha'Choshen (382:2): I answer the Darchei Moshe's question from the Tosfos Rid (Kidushin 42b DH She'ani), who says that Shelichus does not help for a Mitzvah on the body. Therefore, one who can circumcise should do so himself.

Tevu'os Shor (28:14, cited in Gilyon Maharsha 260): When one honors another with a Mitzvah, we do not say that it is a greater Mitzvah to do it himself.

Shulchan Aruch (CM 382:1): If Reuven had a son to circumcise, and Levi did it, he must pay him 10 gold pieces. However, if Reuven asked Shimon to circumcise, and Levi circumcised, he is exempt.

SMA (7): Even though Reuven was able to answer Amen, this does not exempt Levi because the Mitzvah is special for Reuven more than for others.

Shach (4): The Levush says that even if Reuven was Makneh to Shimon, this is Kinyan Devarim, which is void. The Rosh and R. Yerucham say so. Also the Yam Shel Shlomo (Bava Kama 8:60) rules like the Rosh, that Shimon did not acquire. The Rosh clearly forbids a Mohel to give his son to another to circumcise him. The father must do so himself, like Kisuy ha'Dam. The Rambam and Kidushin 29a connote like this. Some people who could circumcise honor others to do so. I say that they are Mevatel a great Mitzvah. Beis Din should be Mevatel this.

Tevu'os Shor (28:14): Shabbos 133a proves that one who circumcises through a Shali'ach did the Mitzvah.

Birkei Yosef (ibid.): The Shach greatly exaggerated. He was not Mevatel the Mitzvah, for one's Shali'ach is like himself.

Ketzos ha'Choshen: The Rema wrote like the Rosh, and exempts one who stole the Mitzvah from the father's Shali'ach. If so, why does the Rema argue with Or Zaru'a, and say that the Shali'ach is like the father? Perhaps since the father showed that he wants to do the Mitzvah through a Shali'ach, the one who circumcised was also the father's Shali'ach. This is unlike Terumah, in which we say that one wants only the Shali'ach he appointed to separate Terumah, for others do not know how much and what quality the owner wants to give. When the father wants to circumcise, no one else is the father's Shali'ach. However, I say that Shelichus requires explicit verbal appointment.

Ketzos ha'Choshen: The Torah imposed Milah on the father. One who can circumcise should do so himself. Sucking out the blood is only for Refu'ah, so one may honor another to do it.

Ha'Makneh (Kidushin 29a b'Tosfos DH Oso): Tosfos asked why a verse was needed to exempt women from Milah. It is a Mitzvas Aseh sheha'Zeman Gerama! The Ramban and Ritva say that the Hava Amina was that she is commanded to arrange to circumcise her son. This is not Zeman Gerama We rule like R. Yochanan, that a woman is Kosher for Milah. Surely Milah itself is Zeman Gerama! R. Yochanan must hold that the Mitzvah on the father is arranging the Milah, but not the Milah itself. Therefore, we need a verse to exclude the mother. This defends the custom that the Shach criticized. Tevu'os Shor learned from 133a that others can do the Mitzvah. I say that it is not a proof. We can say that it is better for the father to circumcise, but this does not overrides the Lav of cutting off Tzara'as. Especially if the father makes a Shali'ach, it is as if the father circumcised.

Gilyonei ha'Shas (Shabbos 137b DH Lehachniso): Rashi (Sefer ha'Pardes 41) says that we bless "Lehachniso", for the father needs only to bring the baby to a Mohel for circumcision.

Shach (7): The Rosh says that Kinyan does not help. Perhaps he means only that Beis Din cannot force him, but he agrees with Maharam that one should not retract, and one who retracts is called a Rasha. He argues with Maharam's opinion that it is a Kinyan due to the custom.

Gra (12): We find that one who promised to give Ma'aser to a particular Levi would not retract (Bava Metzi'a 49a). One may rely on "She'eris Yisrael... v'Lo Yedabru Chazav"

R. Akiva Eiger (DH Chazar): The Yam Shel Shlomo (Bava Kama 8:60) says that if one normally gives the Mitzvah to someone, and promised to give it to him, all agree that he cannot retract, just like Situmta, unless he promised before the baby was born.

Pischei Teshuvah (1): Yad Eliyahu (51) and the Pri Megadim hold like Tevu'os Shor, that even if the father can circumcise, he may let someone else circumcise, unlike the Shach.

Beis ha'Levi (1:10): The Rosh (Chulin 6:8) holds that Milah is primarily incumbent on the father, so he cannot make a Shali'ach for this. Our Gemara seems to say someone else can do the Mitzvah! We must say that anyone can do the primary Mitzvah. There is an additional Mitzvah for the father himself to circumcise, to which Shlichus does not apply. If one does not want to circumcise his son, everyone has a Mitzvah to circumcise him, therefore Shlichus does not apply, just like it does not apply to Milah of converts (Ramban).

Chasam Sofer (Chulin 87a DH v'Chasav): Why does Shelichus not help for Milah, unlike the rest of Torah? The Kapos Temarim explains that a Shali'ach is like the Meshale'ach, but his limbs are not like the limbs of the Meshale'ach. The Torah wanted Tefilin on Ploni's arm, but it is not particular who ties it on. Regarding Shechitas Kodshim, we assess that the Torah wanted them slaughtered, but it is not particular that the owner's hand slaughter them. Had the Torah said only "va'Yamal Avraham Es Yitzchak Beno", we would say that he can make a Shali'ach. However, another verse obligates all Yisrael to circumcise Arelim. We must say that the other verse is a special Mitzvah specifically on the father. Shelichus does not help for this. The Kolbo says that s0h for Kisuy ha'Dam, since "Daber El Bnei Yisrael" makes the Mitzvah incumbent on all of Yisrael. If so, the Torah specified the Shochet to teach that it is particular that he himself cover the blood.