Todays daf discusses the issue of whether a Ger is capable of being a judge. The issue is divided between being a judge for dinei mamonos or for dinei nefoshos. This too is divided into whether the ger comes from "eemoh yisroel" or not.
My question: By definition isn't a ger one whose mother was not jewish? Are there situations where we look at the lineage of the father?
In the usage of Chazal, the word "Ger" may also refer to someone whose parents were not both Jewish. That is the connotation of our Gemara when it states that a Ger comes from a Tipah Pesulah. In order to call the Tipah "Kesheirah," like the Mamzer, both halves of the Tipah have to come from Jews.
There are many sources where a Ger is mentioned which conclude "and if his mother is Jewish...," clearly showing that a person with a Jewish mother may still be called a Ger. (See Bikurim 1:4; Yevamos 102a; Kidushin 76b, 77a; Rambam Hilchos Sanhedrin 2:9, 11:11; Hilchos Melachim 1:4.)
The Rambam rules that only two Halachos require both parents to be Jewish: being a judge in cases of Chalitzah and in capital cases. Even the king of Israel may have a non-Jewish father!
Kollel Iyun Hadaf