Pirates vs. Royals - Home-run overturned
 

I do not know how to imbed videos, so I have provided the link.

Marte's double | MLB.com

Can someone please cite a rule that would change this from a home-run to a ground rule double?

Is it a ground rule application or something else?

The ball did not leave the field in flight. Therefore it's a two base award.

IN FLIGHT describes a batted, thrown, or pitched ball which has not yet touched
the ground or some object other than a fielder.

The wall is an object other than the fielder so the ball is no longer in flight.

Each runner including the batter-runner may, without liability to be put out,
advance—
(a) To home base, scoring a run, if a fair ball goes out of the playing field in flight

Thank you for the reply and reference.

Reading your rule reference, if it hits the top of the wall and then goes over is it considered a home run?

Yes.

FAIR TERRITORY is that part of the playing field within, and including the first
base and third base lines, from home base to the bottom of the playing field fence and perpendicularly upwards. All foul lines are in fair territory.

So strictly speaking the face of the fence is the boundary. If the ball hits the top it has gone over the boundary.

The official MLB ruling is that if it hits the top and goes over it's a HR, if it hits the top and comes back it's in play, and if it hits the top and stays there it's a two base award.

If it hits a yellow line it's in play.

The ball hit the top of the padding and bounced over to one side, the padding is no doubt considered not the top the fence in this park per ground rule". The railing behind the padding out of the park if it hits the top of the railing.

Also, looks to me that the ball came back into the playing field after bouncing off the padding.

Bull pen.

What I am saying is the path from the padding till it left play came back over the field in fair territory.

So what - it was no linger in flight so it isn't a HR.

It didn't "come back" at all. It never left until it was over the bullpen wall. That's the point. It hit the front of the wall (the top of the wall being the railing above where it hit), took an odd ricochet and left the field over the bullpen. Since it did not leave the field in flight, two bases.