כִּ֣י יִפָּלֵא֩ מִמְּךָ֨ דָבָ֜ר לַמִּשְׁפָּ֗ט בֵּֽין־דָּ֨ם לְדָ֜ם בֵּֽין־דִּ֣ין לְדִ֗ין וּבֵ֥ין נֶ֙גַע֙ לָנֶ֔גַע דִּבְרֵ֥י רִיבֹ֖ת בִּשְׁעָרֶ֑יךָ וְקַמְתָּ֣ וְעָלִ֔יתָ אֶ֨ל־הַמָּק֔וֹם אֲשֶׁ֥ר יִבְחַ֛ר יְהֹוָ֥ה אֱלֹהֶ֖יךָ בּֽוֹ׃
If a case is too baffling for you to decide, be it a controversy over homicide, civil law, or assault—matters of dispute in your courts—you shall promptly repair to the place that the Eternal your God will have chosen,
Torah Temimah points to Sanhedrin on “bein dam le-dam.”
בין דם לדם. בין דם נדה לדם זיבה, בין דם בהרת לדם שחין.
English: “Between blood and blood” — between the blood of niddah and the blood of zivah; between the blood of a baheret and the blood of a shechin.
The phrase is understood as referring to difficult distinctions in the laws of ritual impurity of blood.
Derash on the verse (Bavli / Sifrei) — not a formal named middah of the 13. The doubled language is taken as pointing to borderline cases of blood impurity.
Cases that turn on fine distinctions between different categories of blood (niddah vs. zivah, etc.) are among those that may be referred to the high court.