Rashi on Deuteronomy 21:18/רש"י על דברים כ״א:י״ח

1סורר (from the root סור to deviate) means, one who deviates from the proper path of life.

2ומורה means, one who is disobedient to the words of his father, of the same meaning as ממרים in the phrase (Deuteronomy 9:7) “ממרים הייתם”, “ye have been rebellious”.

3ויסרו אתו AND THEY SHALL CHASTISE HIM — admonish him in the presence of three people, and if he still remains refractory they cause him to be lashed through the court (Sanhedrin 71a; cf. Sifrei Devarim 218:11). The refractory and rebellious son is not liable to the death penalty until he proves to be a thief and eats at one meal a “tartemar” (a weight of half a Maneh) flesh and drinks half a Log wine, for it is said of him, (v. 20) זולל וסבא, and in another passage (Proverbs 23:20) it says: “Do not be among wine-guzzlers (בְסֹבְאֵי-יָיִן), among gluttonous eaters of meat” (Sanhedrin 70a; cf. Sifrei Devarim 219:4). — The refractory and rebellious son is put to death on account of the final course his life must necessarily take (not because his present offence is deserving death); — the Torah has fathomed his ultimate disposition: in the end he will squander his fathers property and seeking in vain for the pleasures to which he has been accustomed, he will take his stand on the crossroads and rob people, and in some way or other make, himself liable to the death penalty. Says the Torah, “Let him die innocent of such crimes, and let him not die guilty of them” (Sifrei Devarim 220:3; Sanhedrin 72a).