What is the penalty? If the line of scrimmage is inside the 10, they obviously can’t go 10 yards back because that puts the line of scrimmage in the end zone.
If the ball goes out before the 10, the receiving team can’t field it plus 10 yards, because once again the LOS is in the end zone.
Not in the end zone. If the offense fumbles the ball into the end zone and it goes out of bounds it’s a touchback which gives possession to the defense.
ETA: The reason why that’s relevant is because in the NFL that’s just about the only reason you’d want to knock a fumbled ball out of bounds, rather than trying to recover it. I’d assumed that should be self-evident.