stumbling-block

block out

to prevent (a thought) from entering one's mind.

chip off the old block

Someone who takes after one of their parents; (generally) a person similar to another.

gapers' block

A traffic jam resulting from motorists slowing to look at a motor vehicle collision or other roadside distraction.

knock someone's block off

To strike a person in the head, causing them to fall to the ground, especially in an unconscious condition; to beat up a person.

new kid on the block

Someone or something new to an existing community.