Left-side foot radical - a leg with the foot drawn at the base. Carries the meaning: 蹈 is a foot action - to stamp, tread, dance. Indexes the character in the foot family alongside 跑 to run, 跳 to jump, 踩 to step, 踏 to trample.
Right side 舀 supplies the sound - yǎo drifting to dǎo along an old onset alternation. The 'scoop, ladle' meaning is not transferred; it is purely a sound tag here. Same phonetic appears in 稻 rice plant, 掐 to pinch - chars sharing the central 臼 mortar element.
