The walk radical wraps around the bottom-left and is the indexing radical. Originally a foot crossing a road, here it casts blocking and shielding as something one moves into position - stepping in to cover, hide or shelter - alongside 进, 边, 道.
Sits in the upper-right corner and lends the sound, drifting from shù to zhē. The multitude meaning is unrelated, though a covering crowd is a workable mnemonic - many bodies thronging together form a screen, much as 遮 means to block from view.
