וַיִּֽחַר־אַ֤ף בָּלָק֙ אֶל־בִּלְעָ֔ם וַיִּסְפֹּ֖ק אֶת־כַּפָּ֑יו וַיֹּ֨אמֶר בָּלָ֜ק אֶל־בִּלְעָ֗ם לָקֹ֤ב אֹֽיְבַי֙ קְרָאתִ֔יךָ וְהִנֵּה֙ בֵּרַ֣כְתָּ בָרֵ֔ךְ זֶ֖ה שָׁלֹ֥שׁ פְּעָמִֽים׃
Da erglühte der Zorn Balaks gegen Bileam, und er schlug die Hände zusammen; Balak sprach zu Bileam: Meine Feinde zu verwünschen habe ich dich geladen, und du hast sie gesegnet schon drei mal.
Sforno on Numbers
ויספק את כפיו, as a sign that he had abandoned hope of achieving his objective, seeing that Bileam was cursing those whom he wanted to be the cursers.
Or HaChaim on Numbers
ויתר אף בלק..ויספק את כפיו, "Balak became angry… and clapped his hands, etc." He expressed his anger by clapping his hands together.