drag
挐 centers on pulling something along: dragging or drawing it by hand.
挐 combines 如 (top) and 手 (hand, bottom). The exact historical development is uncertain, but the hand component suggests an action involving pulling or dragging.
A hand 手 below 如, as if a hand is pulling something along like a rope: dragging it forward.
For ダ, imagine dragging a heavy duffel bag: duffel -> ダ, and your hand pulls it along the ground.