עַל־כֵּ֡ן לֹֽא־יֹאכְל֨וּ בְנֵֽי־יִשְׂרָאֵ֜ל אֶת־גִּ֣יד הַנָּשֶׁ֗ה אֲשֶׁר֙ עַל־כַּ֣ף הַיָּרֵ֔ךְ עַ֖ד הַיּ֣וֹם הַזֶּ֑ה כִּ֤י נָגַע֙ בְּכַף־יֶ֣רֶךְ יַעֲקֹ֔ב בְּגִ֖יד הַנָּשֶֽׁה׃
Therefore the children of Yisrael do not eat the sciatic nerve that is on the hollow of the thigh, to this day, because he touched the hollow of Yaakov’s thigh on the sciatic nerve.
Torah Temimah points to Chullin 91a (the angel’s action).
ויגע בכף ירכו — תנא דבי רבי ישמעאל: במקום שחיטת בהמה נגע בו.
“And he touched the hollow of his thigh” — A Tanna of the school of Rabbi Yishmael taught: He touched him in the place of the slaughter of an animal.
The location of the injury is identified with the place of shechitah.
Derash on the precise place of the injury (Bavli).
The angel struck the place corresponding to the site of animal slaughter.