Gemara

(Beraisa): "He will spill (the blood of a Chayah or bird) and cover" - the one who slaughters covers;

R. Gamliel once obligated a man to pay 10 gold pieces for covering the blood of what another man had slaughtered.

Question: Is this for stealing the Mitzvah, or for depriving him of the Berachah?

This determines the fine for 'stealing' Birkas ha'Mazon (when someone else should have blessed.) It is only one Mitzvah, but it is four Berachos.

Answer: Once, Rebbi invited a Tzeduki to eat, and offered him 40 gold pieces if he will decline to drink the Kos Shel Berachah (the wine over which they will say Birkas ha'Mazon). The man declined the money. A Bas Kol announced that 40 gold pieces is the value of Birkas ha'Mazon.

Bava Kama 91b (Beraisa): If Reuven claimed 'you killed my ox' (or) 'you cut my young trees', and Shimon answered 'you told me to do so', he is exempt.

(Rav): A damager cannot exempt himself by saying this! Rather, the ox or tree needed to be killed or cut. Reuven wanted to do the Mitzvah himself.

Rishonim

Rif and Rosh (Bava Kama 32b and 8:15): R. Gamliel made a man pay 10 gold pieces. This is letter of the law, and we learn from it to other cases.

Rambam (Hilchos Chovel u'Mazik 7:13): If the ox or tree needed to be killed or cut because it was damaging people, and Shimon slaughtered or cut it without Reuven's consent, he must pay Reuven like the judges deem proper, for he prevented Reuven from doing a Mitzvah.

Rambam (14): Similarly, if Reuven slaughtered a Chayah or bird, and Shimon covered the blood without Reuven's consent, he pays like the judges deem proper. Some say that there is a fixed fine of 10 gold pieces whenever Ploni prevents David from doing a Mitzvas Aseh that it was proper for David to do.

Question (Tosfos Chulin 87a DH Oh): Why didn't Rebbi offer the Tzeduki 50 gold pieces? He lost four Berachos of Birkas ha'Mazon, and also Borei Peri ha'Gafen on the Kos Shel Berachah!

Answer #1 (Tosfos): He holds that Borei Peri ha'Gafen said during the meal exempts the Kos Shel Berachah.

Rebuttal (Shach CM 382:3): If so, Rebbi is unlike the Amora who requires a new Borei Peri ha'Gafen on the Kos Shel Berachah!

Answer #2 (Shach): Rather, one pays 10 gold pieces only for a Mitzvah mid'Oraisa, like the Maharshal says. The fourth Berachah of Birkas ha'Mazon is only mid'Rabanan. Alternatively, one does not pay for Borei Peri ha'Gafen, for it is a mere Berachah for Hana'ah.

Poskim

Shulchan Aruch (CM 382:1): If Reuven's ox was going to be killed or his tree was going to be cut because it was damaging people, and Shimon slaughtered or cut it without Reuven's consent, he must pay Reuven like the judges deem proper, for he prevented Reuven from doing a Mitzvah.

Drishah (2): The Tur says 'the same applies to any Mitzvah', i.e. even if there is no Berachah.

Shach (1). R. Yerucham (15:4) says that some say that 10 gold pieces is only for a Mitzvah with a Berachah. Others say that it is even for a Mitzvah without a Berachah, for one pays for killing an ox or cutting a tree. The Rashba and Ran conclude that one pays 10 gold pieces for each Berachah, and also for a Mitzvah without a Berachah. We do not distinguish Mitzvos one from another.

Question (Divrei Chamudos Chulin 6:25): If each Berachah is worth 10, and a Mitzvah without a Berachah is worth 10, why does one pay only 10 for a Mitzvah with a Berachah?

Answer (Shach 3): The Gemara proves that this is the law. Since one cannot bless without the Mitzvah, the Mitzvah is included in the 10 gold pieces for the Berachah.

Shulchan Aruch (ibid.): Similarly, if Reuven slaughtered a wild animal or bird, and Shimon covered the blood without Reuven's consent, he pays like the judges deem proper. Some say that there is a fixed fine of 10 gold pieces for preventing David from doing a Mitzvas Aseh that it was proper for David to do.

Beis Yosef (DH v'Chosvu): Tosfos (91b DH vChaivo) cites a case in which a Shali'ach Tzibur called Ploni to read the Torah, and Almoni came first and read. R. Tam told Almoni to give a chicken to Ploni to slaughter (and cover the blood), to compensate for the loss of two Berachos of (before and after Kri'as ha'Torah). The Ri disagreed. If so, why did R. Gamliel make the man pay 10 gold pieces? Further, R. Tam exempted him, for Ploni was able to answer Amen; one who answers Amen is greater than one who blesses.

Kaftor v'Ferach (16): One who steals a Perutah must go to Madai to return it (if necessary), so he will not regularly steal. We should be no more lenient about one who stole a Mitzvah, whose reward is in the world to come! The Torah does not teach the reward for each Mitzvah. Who says that the reward for slaughter and Kisuy ha'Dam equals that of reading in the Torah?! One Mitzvah can change a person and the world from Chovah to Zechus!

Shulchan Aruch (ibid.): Nowadays, we do not collect this. If he seized it, we do not force him to return it.

Tur (ibid.): Nowadays we do not collect this. Even if he seized, we force him to return it, for Reuven answered Amen, and one who answers Amen is greater than one who blesses. If Reuven heard and did not answer, he caused his own loss.

SMA (7): This exemption is only for Mitzvos for which it was enacted to bless aloud in a Tzibur, e.g. for Bris Milah. Then, surely Reuven heard the Berachah. We do not say so about Shechitah. Milah is incumbent on the father, therefore if another circumcised, he must pay 10 gold pieces even if the father answered Amen.

Rebuttal (Shach 4): The source to exempt due to Amen is from R. Yerucham. He exempts even for Milah! R. Gamliel obligated one who blessed quietly.

Yam Shel Shlomo (8:60): It is difficult to say that we discuss a Rasha who denied Reuven the chance to answer Amen. I say that answering Amen does not exempt. One who answers is greater than one who just blesses, e.g. Tefilah or Kri'as ha'Torah. Regarding covering the blood or Milah, which is a Mitzvah by itself even without the Berachah, he pays for the Mitzvah itself. If one seized the fine, he need not return it even if he answered Amen.

Rebuttal (Shach 4): The Gemara concluded that the 10 gold pieces are primarily for the Berachah. Shimon was not a Rasha. He merely blessed quietly!