When the etrog was thrown TB Sukkah 48

 A wine libation (נִיסּוּךְ הַיַיִן) accompanied every sacrifice. Depending upon the size of the sacrifice three, four, or six loggim of wine was poured on the southwest corner of the altar. Each day of Sukkot a water libation (נִיסּוּךְ הַמַּיִם) was also poured on the southwest corner of the altar. According to the rabbis, this water libation was a mandatory mitzvah based on their interpretation of some verses. You’ll see later on in the Mishna why this fact is important.

The second Mishna in massekhet Rosh Hashanah gives a reason why during Sukkot there is a water libation. I’ll quote the entire Mishna because one of the four times the world is judged is on Rosh Hashanah which is less than two weeks away. “At four times of the year the world is judged: On Passover judgment is passed concerning grain; on Shavuot concerning fruits that grow on a tree on Rosh HaShana, all creatures pass before Him like sheep [benei maron], as it is stated: “He Who fashions their hearts alike, Who considers all their deeds” (Psalms 33:15); and on the festival of Sukkot they are judged concerning water, i.e., the rainfall of the coming year.” (Sefaria.org. translation) Unlike Egypt which relies on the Nile River for irrigation and Babylonia which relies on the Euphrates River for irrigation, having no major river to irrigate the land, Israel depends upon the rainfall for a successful harvest. On Sukkot we pray for the proper rain to fall because God judges how much rainfall will fall in Sukkot. The ritual of water libation highlights the importance and the urgency that rain should fall lest a drought occurs.

The Mishnah on daf TB Sukkah 48 details this once a year mitzvah which hasn’t been observed since the destruction of the “Temple by the Romans in the year 70 CE.

“MISHNA: With regard to the rite of water libation performed in the Temple during the Festival, how was it performed? One would fill a golden jug with a capacity of three log with water from the Siloam pool. When those who went to bring the water reached the Gate of the Water, so called because the water for the libation was brought through this gate leading to the Temple courtyard, they sounded a tekia, sounded a terua, and sounded another tekia as an expression of joy. The priest ascended the ramp of the altar and turned to his left. There were two silver basins there into which he poured the water. Rabbi Yehuda said: They were limestone basins, but they would blacken due to the wine and therefore looked like silver. The two basins were perforated at the bottom with two thin perforated nose-like protrusions. One of the basins, used for the wine libation, had a perforation that was broad, and one, used for the water libation, had a perforation that was thin, so that the flow of both the water and the wine, which do not have the same viscosity, would conclude simultaneously. The basin to the west of the altar was for water, and the basin to the east of the altar was for wine. However, if one poured the contents of the basin of water into the basin of wine, or the contents of the basin of wine into the basin of water, he fulfilled his obligation, as failure to pour the libation from the prescribed location does not disqualify the libation after the fact.

“Rabbi Yehuda says: The basin for the water libation was not that large; rather, one would pour the water with a vessel that had a capacity of one log on all eight days of the Festival and not only seven. And the appointee says to the one pouring the water into the silver basin: Raise your hand, so that his actions would be visible, as one time a Sadducee priest intentionally poured the water on his feet, as the Sadducees did not accept the oral tradition requiring water libation, and in their rage all the people pelted him with their etrogim.” (Sefaria.org. translation)

The Mishnah continues, but I just want to point out once again the rivalry between the Pharisees and the Sadducees. The Sadducees for the most part consisted of the priests and the nobility. Many of the early Hasmonean (another name for the Maccabees) Kings were or at least sided with the Sadducees. As the Mishnah notes in the regular font that the Sadducees rejected the oral Torah. Because the water libation is nowhere to be found in the written Torah, they denied that the water libation was a mitzvah at all. The Mishnah records a very famous story when a Sadduceean priest mocked the ritual of the water libation by pouring it on his feet instead of on the altar. The Jews in the courtyard being of pharisaic persuasion were naturally unhappy and expressed their unhappiness by pelting that Sadduceean priest with their etrogim. As you can see there is great animosity between the two sects. Don’t worry, the Sadducees gave as good as they got. Only after the Temple was destroyed and the power base lost, the Sadducees disappeared for good.