Yoko Geri Kekomi or perhaps Ura Mawashigeri?
This is a perfect moment of 'kime', pronounced key-may.
Kime (Japanese: 決め) is a Japanese word. It is the noun form of the verb "kimeru," which means "to decide," "to conclude," etc. In English, it's general meaning is "deciding."
Kime is very important in the japanese martial arts. In shotokan, applying the proper kime, the proper power at that one critical moment is all-important in deciding the conflict.