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 96b.
ת"ר: גיד הנשה בריה הוא, לפיכך אכלו אע"פ שאין בו כזית חייב.
Our Rabbis taught: The sciatic nerve is a complete entity; therefore one who eats it is liable even if it does not contain an olive’s bulk.
The Gemara establishes that the gid hanasheh is treated as a complete beriyah for liability purposes.
Derash on the nature of the prohibition (Bavli).
Eating the sciatic nerve incurs liability even without the volume of a kezayit because it is a complete entity.