Patriots tight end Hunter Henry is pushed out off the end line. He steps back into the end zone and catches the pass. In the NFL, a receiver becomes ineligible to be the first player to touch a pass if he steps out of bounds. Officials will drop a hat on the boundary line to indicate that an eligible player has stepped out of bounds.
Since Henry is reestablished in bounds with two feet, he has illegally touched the pass. The penalty is essentially 0 yards; return the ball to the previous line of scrimmage and the down counts, just as if it was an incomplete pass.
In college, a receiver who does not go out of bounds on his own may re-establish back in the field of play and legally catch a pass. In the NFL, the only time an out-of-bounds player retains his eligibility is if the receiver was put out of bounds by the result of a foul.
So the question here is why the Browns were legally allowed to push Henry out of bounds. Because Patriots quarterback Bailey Zappe was scrambling, this is now a running play, and illegal contact fouls do not apply. (Other fouls such as holding remain.) Defensive pass interference
does become a potential foul if the scrambling quarterback throws a pass. Zappe was still warding off a defender at the point when Henry was driven out of bounds, so this is correctly no foul on the defense. But if the timing was off and it was a defensive foul, Henry would have been eligible to catch the touchdown pass.
