With us so far? OK, now hold tight.
Here's the thing: initially, first base umpire Chris Guccione said the ball, which bounced off a secondary outer wall and back onto the field, was in play. That resulted in the base-running equivalent of a car crash, at the end of which Morse was tagged out. However, replay intervened, and the umpires awarded Morse the grand slam.
Still with us? OK, because here's where it gets weird.
Instead of letting Morse trot home from first base, where he had wound up after the play, the umpires made the runners go back to the bases they had occupied and made Morse go back to the plate so everyone could touch the bases in sequence.
And that requirement led to the funniest GIF of the Nationals' season (click to view in motion).
And here's the video of the whole crazy sequence, if you are so inclined. F.P. Santangelo's incredulity makes it all better.