The yellow line is not an official line its suggestive, if the ball is at the QB's groin area they don't make the 1st, can you or the replay official tell me where the ball is at when his momentum is stopped?
The QB was on top of the pile, he was never considered down. The black line was the line of scrimmage, the yellow was the first down marker. He pushed for 3 whole steps and then slid forward on the pile even more. His whole body was past the black line, and the ref came in, and spotted it on the black line.
It was a terrible spot and replay got it right.