Prometheus is not sluggish as a giant, but his sheer size does telegraph his movements far easier than someone small and swift. He's not surprised that Thor escapes his open hand slap, and quickly draws his arm back so that Thor can't use it to climb on him or throw him off his stride somehow.

He turns, attempting to follow Thor's sprint, but he's too slow, and Thor succeeds on getting a grip on his greaves. The Titan's solution? He slams his foot as hard as he can into the earth in an effort to shake Thor off from the sheer force of it.