وَكَيْفَ يُحَكِّمُونَكَ وَعِندَهُمُ ٱلتَّوْرَىٰةُ فِيهَا حُكْمُ ٱللَّهِ ثُمَّ يَتَوَلَّوْنَ مِنۢ بَعْدِ ذَٰلِكَ ۚ وَمَآ أُو۟لَـٰٓئِكَ بِٱلْمُؤْمِنِينَ
Wa kaifa yuhakkimoonaka wa 'indahumut Tawraatu feehaa hukmul laahi summa yatawallawna mim ba'di zaalik; wa maaa ulaaa'ika bilmu'mineen
But why do they come to you for judgment when they have the Torah, in which is God's judgment, and then turn away after that? Such people are not believers.
Yuḥakkimūnaka is the verb for appointing someone as arbiter, and the verse asks why that appointment is being made at all. A book they accept is already in their hands, and two verses earlier the condition they attach is quoted aloud: accept the ruling if it favours them, take warning if it does not. Arbitration sought on those terms is a search for a second opinion.