What I know for sure TB Shabbat 141

We finish the 20^th chapter of massechet Shabbat with daf TB Shabbat 141. Who hasn’t accidentally stepped in a mud puddle walking to or from shul! The amora’im argue whether one is allowed to clean the mud off his shoes on Shabbat.

“Abaye said, and some say that it was stated by Rav Yehuda: If one has mud on his foot, he may wipe it on the ground on Shabbat, but he may not wipe it on a wall. Rava said: What is the reason that he may not wipe it off on a wall? Is it because it appears like building, as he is adding plaster to the wall? That is the building of a field laborer, which is not an actual building. There is no concern in that case because in adding plaster to that building, one does not perform the prohibited labor of building. Rather, Rava said: On the contrary, He may wipe it on a wall, but he may not wipe it on the ground. This is due to the concern lest one come to level holes in the ground while wiping his foot. It is stated that other amora’im disputed this issue. Mar, son of Ravina, said: Both this, wiping the mud on a wall, and that, wiping the mud on the ground, are prohibited. Rav Pappa said: Both this and that are permitted. The Gemara asks: According to the opinion of Mar, son of Ravina, with what may he wipe his foot? The Gemara answers: Even according to his opinion, there is a permitted manner to clean his foot; he wipes it on a beam on the ground.

“With regard to mortar that is on one’s shoe, he may scrape it off with the back of a knife as a departure from the typical manner of scraping…Rabbi Abbahu said that Rabbi Elazar said that Rabbi Yannai said: One may scrape mud off of a new shoe on Shabbat, but not off of an old shoe, because a layer of the shoe will be removed, which constitutes the prohibited labor of smoothing. With what does one scrape it off? Rabbi Abahu said: With the back of a knife, which is a departure from the typical manner of doing so. A certain Elder said to Rabbi Abbahu: Delete your teaching before this statement taught by Rabbi Ḥiyya: One may not scrape at all; neither a new shoe nor an old shoe…” (Sefaria.org translation)

The amora’im disagree amongst themselves with some completely forbidding removing mud from one’s shoes on Shabbat, some permitting to clean new shoes in a different manner like using the back of a knife or on a wall or on a beam, and some permitting one to clean his shoes in any fashion he chooses on Shabbat.

The rishonim also disagree whether one is about to clean off mud off on Shabbat. The Bet Yosef (Joseph Caro) rules that one is only allowed to clean off the shoes on a wall, but not on the ground lest one level holes following Rava’s opinion. The Rif only allows a person to clean his shoes on a beam following the opinion of Mar, son of Ravina. The Rosh following Rav Pappa’s opinion decides that one may clean his shoes even by wiping them on the ground. (See Shulkan Aukh, Orekh Hayyim, 302:6)

Now you know that the answer to the above question is as clear as mud. All I know for sure is that I better not track any mud into the house!