TT #788 · Parashas Ki Seitzei · Seventh Aliyah · Passuk 25:18
how he happened upon you on the way and cut down all the stragglers in your rear, when you were weary and exhausted, and he did not fear God.
Torah Temimah points to Sifrei / Shabbos.
TT lemma: כָּל הַנֶּחֱשָׁלִים אַחֲרֶיךָ.
מְלַמֵּד שֶׁלֹּא הָיָה הוֹרֵג אֶלָּא בְּנֵי אָדָם שֶׁנִּמְכוּ מִדַּרְכֵי הַמָּקוֹם וְנֶחֱשְׁלוּ מִתַּחַת כַּנְפֵי הַמָּקוֹם.
English: This teaches that he killed only those people who had fallen away from the ways of the Omnipresent and had become weak from under the wings of the Omnipresent.
On the daf / in context: Amalek targeted the stragglers — those already spiritually or physically weakened.
Derash identifying the victims as the weakened stragglers.
Amalek’s attack was directed at the vulnerable rear of the camp, those who had fallen behind.