Or HaChaim on Numbers 24:10/אור החיים על במדבר כ״ד:י׳

1 ויתר אף בלק..ויספק את כפיו, "Balak became angry… and clapped his hands, etc." He expressed his anger by clapping his hands together.

2ברכת ברך, "you have surely blessed." Balak meant that the blessing he heard Bileam pronounce was not the kind that was a curse in disguise. He proved this because Bileam had said that anyone who blesses Israel (in this fashion) was to be blessed himself, etc. Clearly, Balak had not understood the nuances of Bileams's words we have explained as reflecting his evil intent even here.