辶 is the motion radical 辵 in its bottom-left walking form. It marks 违 as an action of going — but here, going against, deviating, walking in the wrong direction. Sister verbs 进, 退, 过 share the radical and the moving-feet signal.
韦 (wéi) supplies the sound exactly — identical reading. Originally pictured two feet walking away from a town in opposite directions, so it also carries a faint go-against flavour that reinforces 违's meaning of disobeying or violating. Powers 围 (surround), 伟 (great), 纬 (latitude).
