Pay closer attention. They’re not past the line until the pass is thrown.
You’re correct – that rule was the focus of the controversy around Franco Harris’s “Immaculate Reception” catch in the 1972 divisional playoff against the Raiders.
The officials ruled that Raiders defensive back Jack Tatum had touched the pass after it had bounced off of Frenchy Fuqua, before Harris caught it. If Tatum hadn’t touched it (and Tatum maintained that he hadn’t), Harris couldn’t have legally caught the ball.
The Wikipedia article on the play notes that the rule was repealed before the 1978 season.
Linemen can block down field if the forward pass does not cross the line of scrimmage. That’s how it works for screen passes, the pass is thrown behind the line.
This is not a true statement in the NFL. See the previously linked NFL rules book.
My bad. It is definitely allowed in college though.