[1] Weak side linemen will sometimes pull and lead the back downfield (sometimes called a counter trap), but not necessarily.
The play is designed to get the defense to flow away from the action for a few steps, allowing better blocking angles for the offensive line, and more room for the running back.
The purpose of the counter run is to keep defenses honest and prevent them from easily being able to pursue the play aggressively.
This play is designed for the offensive team to feign rushing one way, then attack the defense in the opposite direction.
[2] In particular, guard Russ Grimm and tackle Joe Jacoby would open up massive holes for John Riggins, George Rogers, and Earnest Byner.