Punt behind neutral zone

[Robert Goodman]

While the ball is behind the neutral zone, if the kick was still in flight at least Fed and NCAA codes agree on this. Opposing players going for the ball may use contact -- including the hands, as long as not holding -- to knock each other out of the way in a personal attempt to get at the ball. The fair catch is off, no matter where it was signaled, but there's no penalty for having signaled ineffectually, so players of either team on gaining possession of the ball may advance it. The clock status is the same as it would have been on any other play where team A leaves the ball beyond the line to gain.

I think NFL may have a different ruling wherein the kick penetrates the plane of the receiving team's neutral zone even temporarily and in the air.

In Canadian football it's possession to the receiving team where K3 recovered if K3 was offside, but no penalty for "no yards" if the ball was behind the line of scrimmage. If officials saw the collision likely to develop between a receiving player and an offside player, they'd blow the play dead with the ball still in the air, spotting it at the point where the ball came down, possession to the receiving team. If K3 was onside, the rulings would agree with Fed and NCAA.