What semantic notions underlie 遮 (obstruction) with 辶 (walking)?
One of the meanings of 遮 is &quot;obstructing&quot; - getting in the way of somebody else, thus preventing them from walking. That might be the reason why 辶 (walking) was chosen as the semantic component.
As for the usage of 遮 in Cantonese: It is easy to make a connection between &quot;cover, shield&quot; and &quot;umbrella, parasol&quot; because umbrellas/parasols are used too shield oneself from the rain or sun.  In fact, &quot;para&quot; in &quot;parasol&quot; or &quot;parapluie&quot; (French for umbrella) means &quot;protecting against&quot;.