This surprisingly contemporary point of law came up during the rabbis’ discussion of an extremely ancient ritual—a combination of the remote and the familiar that feels characteristic of the Talmud. Since the beginning of Tractate Yevamot, which deals primarily with levirate marriage, we have heard that although a man is legally obligated to marry his dead brother’s widow, there is an escape clause. If either party doesn’t want to go through with the marriage, they can perform the ceremony called chalitza, or “removal.” The form of this ceremony is spelled out in Deuteronomy: In front of a court of elders, the woman must remove the man’s shoe and spit in front of him, while saying, “So shall it be done to the man who does not build his brother’s house.”The passage in question is Deuteronomy 25:5-10. I don't know what the rabbinic rule was, but the rule in Deuteronomy is rather more confrontative, in that the woman spits not in front of the man, but in his face. (The two Hebrew expressions are almost the same, but the only reason for reading the specific wording of the passage as "in front of him" is to try to tone down its most natural meaning.) That said, in the only place in the Hebrew Bible when the rule is actually implemented, Ruth 4:1-12, the sandal transfer is between the two men and there is no spitting involved. So it looks as though even the ancient Israelites may have thought that Deuteronomy's version was over the top.
Earlier Daf Yomi columns are noted here and links.