Left foot radical, the indexing element — pictograph of a leg and foot, the upper 口 the knee and the lower portion the planted sole. Marks 跃 as a leg-motion verb: jumping, leaping, springing. Same family as 跑, 跳, 踢, 路.
Right 夭 supplies the sound, drifting yāo → yuè (traditional 躍 used 翟 instead — the simplified swap cut strokes). 夭 pictures a person with bent head, a posture of motion or bowing — fitting for a leaping action. Same phonetic in 妖, 沃.
