עַל־פִּ֨י הַתּוֹרָ֜ה אֲשֶׁ֣ר יוֹר֗וּךָ וְעַל־הַמִּשְׁפָּ֛ט אֲשֶׁר־יֹאמְר֥וּ לְךָ֖ תַּעֲשֶׂ֑ה לֹ֣א תָס֗וּר מִן־הַדָּבָ֛ר אֲשֶׁר־יַגִּ֥ידֽוּ לְךָ֖ יָמִ֥ין וּשְׂמֹֽאל׃
You shall act in accordance with the instructions given you and the ruling handed down to you; you must not deviate from the verdict that they announce to you either to the right or to the left.
Torah Temimah points to Sanhedrin / Sifrei.
אשר יאמרו וגו'. מלמד שצריך שיאמרו לך את המשפט.
English: That they say to you — this teaches that they must state the judgment to you.
The ruling must be explicitly communicated to the parties.
Derash on the verse (Sifrei) — not a formal named middah of the 13.
The parties are entitled to hear the court’s decision stated clearly.